From the sounds of it, you have a "hormonal" mare or what we fondly refer to as PMS (Pissy Mare Syndrome). Although not all mares fall into this category, many mares do and it seems to me to be a little worse when they are younger. Having trained quite a few mares that fall into this category, I'll tell you about my multi-faceted approach.
First, I would put the mare on a supplement to help stabilize her hormones. I have had some success with supplements designed to calm an anxious horse; there are many great ones on the market; consult with your veterinarian about choosing one. Before the days of great supplements like this, horseman commonly bred hormonal mares in order to stabilize their hormones. I have an exceptionally hormonal mare in training right now and I am happy to say she has made awesome progress, but not only did we put her on a supplement, we also bred her.
Secondly, you have to understand these mares and how territorial they are. They are especially defensive in their stalls or when a stranger approaches them. We are so used to trained and gregarious horses that we routinely barge into a horse's space- just walk right up unannounced and pat them on the neck or head or rump. You can't treat a hormonal mare this way. You need to approach her slowly and gently and make sure you introduce yourself before you barge right into her space. As you approach her, come only so close (however close that she notices) then stop, divert your eyes and reach out your hand, palm down, for her to approach you and smell your hand. Taking this little bit of extra time when you approach her will help a lot toward her defensiveness.
As she gets more comfortable and trusting of you, she will accept your closeness better. Along the same lines, these mares need a lot of space and do not do so well when you crowd them. Again, we are so used to horses that will tolerate us in their space that we tend to be too close to the horse all the time, hanging on his neck, smooching his face, etc. Give this mare lots of room, always ask before you enter her space and try to keep a comfortable distance from her as much as possible.
The third facet in dealing with hormonal mares is the training. This can be pretty tricky, especially if you do not have much experience (see other Q&As on green riders and green horses). These mares need to learn obedience through lots of groundwork, but they tend to be very irritable and it is easy to escalate the irritability rather than instill obedience. You have to tread a fine line between discipline and correction and leaving them alone when they behave, with a very heavy dose of patience. As I do with all horses, I like to teach the horse some very basic rules of behavior and with consistent correction; the horse will learn the rules very quickly.
The first rule I like to work on is that the horse will stand absolutely still when I ask her to. I practice this with a rope halter and 12' lead (if you need one, I have the brand I prefer for sale on my website www.juliegoodnight.com), standing out in the open and asking the horse to stand by saying "whoa" and standing to the front and side of the horse with my toes facing the horse's shoulder.
The way you position yourself in relation to the horse is critical, as the horse will quickly learn to associate your toes facing toward her with her not moving. I will not try to stand close to the horse or choke up on the lead in attempt to hold the horse there, I want her to stand there on her own while I keep a fair distance from her. Every time she makes a mistake and moves, I will say "whoa" and pop the lead; if she has moved substantially I will put her feet back where I asked her to stand to begin with by backing her up. Horses are very aware of how and when they move their feet, and will typically be moving in a direction they want to go (like toward the barn), so it is important to put her back where you told her to stand.
I will also work on making the horse stand still at the hitching rail while I am grooming her. Often, these mares can be very fussy and fidgety, so usually I will attach a second lead to the halter and hang onto it as I groom. If the horse moves her feet at all, I will firmly say, “whoa,” and give a sharp pop on the lead. Again, consistent correction will improve the horse very quickly. If she moves substantially, I will place her back where she was and tell her, “whoa..” Keep in mind that often hormonal mares are quite sensitive, so be careful you are not putting too much physical pressure on her while you are grooming.
Now for the important part: don't hassle the mare, don't pick on her, just trust her to stand; leave her alone when she does and correct her when she doesn't. Most PMS mares do not care much for being rewarded by a rub on the neck or praise, but they do appreciate it when you leave them alone. Whichever reward your mare prefers, be sure to offer it when she makes the slightest attempt to obey.
The next basic rule of behavior I will work on is keeping her nose in front of her chest at all times when I am working around her on the ground or riding her. Again, to achieve this you only need consistent and gentle correction. Every time the nose moves away from me, I give a gentle bump of the halter rope until it comes back to center. When the nose moves toward me, it is a bigger infraction because the mare is moving into MY space, so I will twirl the end of the lead toward her nose to push it back where it was (in short order, all I will have to do is point at her nose to move it back).
There is much more groundwork to accomplish on the lead line and in the round pen, but the main thing with a mare like this is to insist on obedience without nit-picking and nagging the horse. Be patient and trust the horse to obey. If you aren't patient and don't have faith in her, you will start picking on her and getting irritable and quick yourself and since horses mirror our own emotions, this will escalate her irritability.
In answer to your final question, while some geldings can be a little challenging, on the whole they are much less challenging than mares. In the natural herd setting, a mare is generally at the top of the pecking order and the "boss mare" is responsible for keeping discipline in the herd and watching out for the safety of the herd. So by nature, mares tend to be more dominate and controlling than geldings. Another important factor is that geldings are neutered and mares are not, so the hormones become an issue. I would never suggest that you get rid of this mare without seeing you and her work together, but I would say that a well-trained older gelding would be much easier than a young hormonal mare for an inexperienced person to work with. Good luck and be safe!
Julie Goodnight, Clinician and Trainer
If you liked this article, Julie suggests the following products to help you continue the work with your horse (or call 800-225-8827 for ordering help):
From the Ground, vol. 1, Round Pen Reasoning: http://www.shop.juliegoodnight.com/shop/trftg1roundpenreasoning.html
FTG, vol. 2, Lead Line Leadership: http://www.shop.juliegoodnight.com/shop/trftg2leadlineleadership.html
Basic Ground Work Package: http://www.shop.juliegoodnight.com/shop/packagebasicgroundwork.html
Goodnight's Complete Groundwork Package : http://www.shop.juliegoodnight.com/shop/packagecompletegroundwork.html
You may also enjoy working with Julie to help conquer your goal at a Clinic Tour stop. Click here to ride or watch a clinic. http://juliegoodnight.com/clinics