Requested to be anonymous.

First of all , how old are all of you ?  I must say that i agree about the fact that your friend sounds alittle too suspicious to the point that some of her statement makes me think twice before believing .

The only way for you all to know the truth is to honestly talk to her face to face with a confrontation . I think it would be better if the closest friend to her ( either B or yourself ) talk to her instead since it might be intimidating if both of you go to her at once .

However , if she doesnt want to tell you , dont give her pressure and force her to . Respect her decision .

Let her know that both of you felt the same way whenever she tells you guys about her cutting , her boyfriend .... at least , Friend A would know about it and she can address the matter to you .

At the end of the day , its your choice to choose to believe her or not .  Good luck !!