What's the best way to put weight on mini mare nursing a foal?

when I got her about a month ago she was severly underweight and her hooves looked like elf shoes I got her feet fixed and wormed her.I got some rice bran cause somebody told me that would put weight on her,but she wont eat it.she want eat carrots or apples the only thing she will eat is hay and sweet feed.How can I get her to eat the rice bran or something else to build her weight back up while she's nursing and how much of it,she is a mini about 30 inches tall