Selling my mother's house in another state....

I live in Vermont and own half off my elderly mother's house in Massachusetts as she added my name to the deed in 2017 and she is the life estate owner. She wants to sell it now,  and If I agree to sell, how do I figure the capital gains tax and what are all the forms I need to file federally, with Vermont, and the state of Massachusetts ? My Home and Business software isn't very helpful.