It sounds like mom has had about enough of the baby. I'm going to preface the next bit with the caveat, I don't raise minis, don't know if you feed them way differently from regular horses, so take what I say with a grain of salt and maybe consult with your vet.
I would not feed my mare or the foal Safe Choice because I want my lactating mare and the foal to have a minimum of 16% protein. My full sized mares eat an INCREDIBLE amount of mare and foal feed, starting approximately 2 months before foaling. A lactating mare will eat 12 1/2 lbs of the feed I use to maintain 1000 lbs and build up a good bag. Once the foal is born, I keep mom on 12.5 lbs of feed plus free choice hay while the baby is nursing. I will add a couple of pounds if mom starts to lose condition.
Once the baby starts to be interested in mouthing solid food and starts stealing from mom's pan, I tend to put a little bit in a separate pan just so baby learns to start eating a little ways away from mom. LONG before I'm ready to wean. As for hay, I let them eat what they want when they want but I've noticed that at first they don't seem to eat much hay, they don't know how to chew it, it seems.
When they come in like little tanks and BAM, headbutt into mom's udders, it can't feel good and none of my mare's will tolerate that. They will squeal, grunt, move away, kick or bite the youngster (gently, not kick across the stall or anything) to teach some 'table manners'. I have one mare that at 3 months is getting tired of her little succubus and by the time 4 months comes along, that's it, the milk bar is CLOSED. She loves having the baby around is takes very good care of the foal but after 4 months, they get their own rations and she stops lactating.