I use Mare Magic on my mare, and I find that it is definitely worth the money. Even though it's quite pricey, it lasts forever on a maintenance dose, literally a bottomless pit. I have a 7 y/o mare who I have owned for 2.5 years, she had basically been in a field on her own a good majority of her life, with minimal human or animal contact, and none what-so-ever for the year before I bought her. She really had no idea how to interact with humans or other horses when I bought her, and I couldn't really blame her. She was very finicky with other horses being near her, still can be, but it used to be to the point I'd walk her past a stall and she'd try kicking the horse's head in. Riding with other horses was NBD, but if a rider brought their horse much too close my mare would kick/lunge/whichever end came first (I made, and still make others in the arena aware that she is a kicker and please do not come too close to her butt/face, some riders choose to ignore this) - this is something we are working on and has gotten loads better.
Bottom line, since I have stuck this mare on the Mare Magic she has been 100x better with other horses. She has always been a quiet mare in general, I could stick a baby on her and come back an hour later and they'd be exactly where I left them. She just really was not socialized as a baby and because of that she really appreciates her personal bubble.
I would definitely recommend giving Mare Magic a shot. Rule out any health issues first, of course.