Interested in a girl but don't know how to get closer to her(COMPLICATED RELATIONSHIP)?

I know this girl im very much interesred in and have no idea how to get closer to her.Heres the complicated stuff, ive known her for years through my friend. she lives in my friends house for complicated reasons so i see her when ever i go over his house. when i first met her she was a lesbian and dated my friends sister, yes the same friend shes liven with. they broke up a few years ago but she still lives in the house as part of the family.even though ive known her for years our relationship is only as far as acquaintances.the thing that bothers me the most is that shes a lesbian so i dont know if she would hate me if i tryed to flirt with her.so what do you think should i try harder or give up?