first time owner urgent help needed

HI all
My daughter got her first horse in December a 13 yr old mare who is 100% in every way, or so we thought until we turned her out in the field!
When we try to catch her she is very aggressive (biting and kicking)towards the other two horses in the field.
Someone on the yard said it may be because she is in season, ( how can we tell if she is in season)
If this is the case has anyone any advise on what we can do. Her tempermaent is fantastic except when in the field.

Hi ya, sounds like your girl is a very mareish alpha or dominant mare..you could help that by paddocking/pasturing her alone, for everyone's safety. In season mares often present with squirting and tail high with winking (you will know what I mean when you see it!) and intense marey behaviour....you can't really change that, I think there are drugs and remedies that can lessen the behaviour but personally if it does not effect any aspect of the horse/rider relationship then I wouldn't bother....in fact I don't like the idea of drugging at all..just my opinion. I would paddock her alone where she can see others but can't hurt them....it maybe helpful, although a nice quiet gelding to be with her maybe helpful too.

Your mare sounds like she may be in season. That's not the main
Issue. Here is what I do. I never go after or chase my horses. They love to play games ! You are either a game piece to them or dinner comming. I have ten mares in one pasture. When they have foals they are even more suspicious of you. Walk in, sit on a five gallon bucket, let them, come to you. Most of the time I have sliced apples or carrots, or horse cookies in my pocket. Always a brush too. I always give them happiness and pleasure FIRST, before I catch, worm, or vaccinate anyone. Remember, safety first. Horses are jeaoulous of each other and the love you are bringing. Know who your dominant horses are, they are usually the ones who come first and run the others away. They want all the love and food. I have so many, I have to get the dominant ones out of the way so I can spend time with the lessor dominant ones. I place my lead rope under my shirt, place it arround the neck of the dominant mare and tie her away or stall her , so I can catch the one I want. It takes time and patience. I don't know everything , but, this has worked for me for years. The longer you have them, the more they trust you.
Good Luck

If it lasts more than a week, and if you don't see any of the signs of her being in estrus that were mentioned, I'd say she's just a dominant/alpha mare. I've had two of these personalities here; one is here right now. When first introduced through fencing everything is fine. Once on the same side of the fence, she goes after everyone with both barrels!

There are two things you can do. First, just keep her seperate. May mean you'll need to feed her year around, but it'll keep the other horses safe from her feet and teeth. Second, make sure there's plenty of room for everyone to stay out of her way and eventually they'll work it out. Of course, there's the risk of others getting hurt in the meantime...

My first alpha mare had 17 hand warmbloods cowering for a couple of months (she was just 12.2!) before she finally began tolerating them. The current filly here right now still let's her feet fly and as a result spends a lot of time in solitary confinement

Thank you v much for your advice :)