Friend confesses she is bisexual?

[Jessy M.]

my friend confesses to me she is bisexual .. and she's all worried about it she feels bad about herself for thinking that she is .. She and two other girls got the idea to text this girl who was lesbian just to mess around.. my friend was pretending to be another girl which was wrong .. and she got more into it and seems to have developed feelings for this girl .. she asks me for advice but i dont know what to tell her