No, I don't think so. A sounds like the possibility of being at home or not, B sounds like giving permission to stay at home or not. C sounds a bit strange with "at home" but if you said "Mary may not be staying at the hotel not" it would sound like it was referring to possibility again.
(a) Mary may not be at home now.
=> She's probably not at home now.
(b) Mary may not stay at home now.
(c) Mary may not be staying at home now.
=> She might stop living at home from now on. (Maybe she had a big fight with her Dad.)