What does this text symbol :B?

It means she is too stupid to use actual words to communicate with. She is operating on the level of a prehistoric cavewoman who communicated by painting pictures on the wall.

It can mean she's being goofy. That face tends to symbolize two bucked teeth, as a form of being goofy. So it is likely that your friend is just being silly.

i think of it as like a monster

A big smile