Hi -- I would ask how long you had mama & baby separated? I usually go with at least 3 months of separation. I'll try putting them back together then & if the weaning hasn't taken, the baby will go out again for a few more months. Usually works.
Some moms tell their babies absolutely no nursing after the first separation. Others, and we've had a very few, will let any body's babies nurse anytime! We had one mare that while she had a new baby, backed up to the fence (split rail at the time) with her hind end, so her yearling baby could nurse too. You just have to take each case as it comes. They are all different.
Another thot, altho it seems to be different that rabbit's approach, I have an area we called the "howdy pen" that we have many uses for. One of the uses is for babies being weaned. It's cattle panel fencing, like all of our fence. Babies & moms can feel, see, smell & hear each other. they can hang out on different sides of the fence, but still be together but there's no nursing possible. This seems to be easier emotionally on both mama & baby. Gradual. but not too drastic. At first, there's a lot of "togetherness." After a few days, neither seems to care too much.
Also, our babies are on full ration of feed & hay at weaning. They are introduced to both the day they are born. Of course, they don't eat much then, but by two weeks, they have their own feeders that mom can't get into.
Again, I think the whole process of weaning has to be geared to each mare & foal. We've almost never had a problem, except maybe a few over the years (80-100 foals). We did have one a few years ago -- the baby got pneumonia almost instantly upon weaning. I immediately put baby back on mom. When vet came, yeah, he said I was right, it was pneumonia, and putting them back together was the smartest thing to do. I figured any less stress on that baby would help her. She recovered, with vet's help. But it was scarey. They are all different.