First you need to make sure she is in a smaller pen (16ft X 16ft. would be good). Something that will be easy to catch her in. I would also suggest you (or get help if needed) and put a break away halter on her with a short lead one that does not drag the ground but hangs down giving you something to grab onto. You really need to get a handle on the mare otherwise you will have a hard time dealing with the baby. There are several things that should have been done and need to be done prior to foaling. At one month prior she needs to have a 6way and west nile vaccine and be dewormed that was she can pass the immunity on to her foal. Also you will need to make sure you keep the placenta for the vet to look at when they come out to do the post foal check. This exam is to look at the mare, the placenta (making sure it all passed so she doesn't get sick), and the foal. An IGg test should be preformed on the foal making sure the foal got all the colostrum that it needed. Also, you will need to dip the umbilicus at least 2-3 times a day with Nolvasan solution the first couple of days. Yes, to answer your question, a mare that is hard to catch and not all together tame can be aggresive towards you and not let you near the foal to do what is needed. I would potentially look into finding someone (trainer) that can help you with your mare and her foal when the time comes. Even if she is just a pet you should be able to handle her and do what you want to with her, without her putting up a fuss. I hope everything works out for you but I would recommend getting some help with her. I have seen mares like this with my job and if by chance your foal gets sick and needs to be handled or even the mare herself these mare are and can be very dangerous to mess with. We had a mare come into the clinic with a newborn foal at here side and they had never been handled well just fed and groomed (when the horse felt like it). The owners were able with help of us and other to run the mare and her foal into a trailer to bring them into the clinic after they had been attacked by dogs. We had to pen the mare up against the trailer wall to give her some IM sedation and had to wait for it to take affect before we could unload her at the clinic. Once sedated we placed a halter with a 3ft lead on her and got her fixed up and in a stall and then we started on the foal. Once we put them together back in the stall the mare made it impossible for us to treat the foal every two hours for its needed treatments. The mare would run around the 12X16 stall like a crazy thing and nearly running over us and her foal. We ended up taking the foal away from the mare and bottle feeding it after about a week. The foals side had be torn open at the flank and required lots of treatment that we were unable to do safely when it was with the mare. The owners of the mare gave her away and the foal ended up coming home with me to live after living at the clinic for about 4-5 months. He is just a pet and is not used at all do to the injury but he is treated like all my other horses and I can do what I need to with him. Hope this info helps and good luck.