Tell her never to give him treats by hand, that should help with the nibbling problem. An equine that is comfortable crowding and nibbling is also comfortable running flat over a person. Reared up on as in tried to mount her? Yes gt him castrated but if she isn't confident in teaching him the basic ground manners it would probably be good to get some professional help.

"It's really quite amazing what a horse will do for you, if he only understands what you want. 
And it it's also quite amazing what a horse will do to you if he doesn't." ~ Bill Dorrance