Sounds OK to me. I fed the same thing I always fed, just added Calf Manna for the month before foaling and about 3 months after to make her milk good.
The thing about feeding is a lactating mare will need alot more then even just a pregnant mare. Mares can go down fast while lactating. I wouldn't just suddenly increase her feed, but she will need to be increased or she will go down and start to look bad.
Alot of people will just let the mare go down, then build her back up after they wean. The mare will go down rather then baby suffer. I just don't like for my horses to look like that.
I feed complete pellets, which means the hay is in the pellets. Normally and while pregnant my mare got about 1 1/2 cans 3X a day, (3lb coffee can). Over the first month while lactating she was increased to 2 cans 3x a day. Plus the calf manna. She never looked bad.
So depending on what you are feeding now, I would start increasing her some for the next month.
ONe more thing. I don't mean to nag about this, but it is very very important to spray the navel with iodine. You haven't said if you have done that, so that is why I'm repeating. They can really get some nasty illnesses/death if you don't do that. I have a friend who didn't do it and it cost her several thousand in vet bills. And I have a feeling this horse could have problems with soundness once she starts to ride him. He got joint ill.
Becky
I've sprayed.sorry, should have told you!
Heh.... well, by reading Becky and my feeding instructions, you can see that there's a lot of options. Most important thing is to make sure mom is getting enough to feed both herself and baby, either through oats and calf manna supplement which is good, or through a feed designed and all measured for nursing mares, which is also good.