WHO gets to decide "how far is too far" ?  I say SHE gets to decide.  And it would not surprise me if she is bothered by the teasing - whether you think it is in good taste or not.  If she is bothered by the teasing,  don't do it. 

She may brush off the teasing, and pretend that she is not bothered by it.  But deep down inside,  she might feel different.  I said, a good friend is going to make the effort to discern whether she is bothered by it, and if so, a good friend will refrain.