I've been through a similar situation twice with my horses, you have every right to be concerned.
I had my 2 mares boarded at a friends, she had 20 acres of pasture 6 horses of her own and a mare/foal that belonged to another friend. This mare that belonged to another friend was very aggressive especially when she seen someone driving up or walking up to the gate, feeding time was a nightmare. We ended up stalling her and her foal separately when it was feeding time which fixed some of the problem however she had one mare of her own that could be down right nasty and she was the type that really tried to hurt the other horses. It got so bad I wouldn't let my youngest out of the truck when we went to feed afraid she would get caught in the cross fire, and while I got the feed together my oldest stayed by the gate with a whip to keep them back.
A couple months go by and I go out to feed one evening and my QH mare is limping I see a huge cut right across her back right coronet band from the barbed wire at that point I figured it was from kicking out at this other crazy mare and decided I better find someplace else to move them before they ended up seriously injured...well while in the process of trying to find another place The friend gets this gorgeous TB gelding and another pony. One evening we go out and I notice the gelding is down in his hind quarters, he can barely walk the owner isn't home I'm trying to round up all the horses get them fed fight with this one mare keep everyone from getting hurt, he won't come up to eat so I walk out across the pasture to see what exactly is going on with him. I was horrified both back legs were swollen almost twice the size they should be he had blood that had run down the back of his right leg, to put it bluntly I didn't think he was going to make it he was beat up really bad. I was furious even though it wasn't my horse. When I finally got a hold of the owner I asked her what happen and she told me her mare had attacked him, I told her point blank if you don't do something with that mare she is going to kill one of your other horses or mine. I had been talking to this guy about renting a small pasture from him and I called him and asked him can you come get my horses we moved them that night, I offered to buy the gelding from her very cheaply of course since I didn't know if he was going to live or not or if he would ever be able to be rode again she declined my offer I moved my horses and that was that. None of the injuries to my mare or this gelding took place when we were around as far as the mare that belonged to another friend she aborted a foal around then to my guess from fighting with this other mare but who knows. He came and got her and the foal she had with her as well. So to sum all this up if there is anyway you can move your horse or have this other mare separated from her it would be wise to do.
You said you have already been kicked as sorry as I am that has happened it could have been your chest or your head lord knows how high a horse can kick. Taking a whip with you will probably curb the problem at the gate but there is still the times something could go wrong when no one is around.
Courage is being scared to death but saddling up anyway~~John Wayne