I did have some of the same reaction that Alcearos did, with the language that was used to describe your friend. It came across as sort of condescending and not really understanding where she's at, who she is, or what strategies SHE can employ. (I have no doubt YOU could handle this stalker, because your personality is different, but she's highly vulnerable because of her past and her personality.)
I didn't think the man broke the door, I was perceiving he just forced his way in. Really, what's a woman to do at that point except for macing him or screaming or making a HUGE deal... which would embarrass her, possibly provoke him, and draw lots of attention she doesn't want? For an ISFJ, such things would just highly embarrassing.
You have to remember, if you look at the three anxiety-reducing strategy, she's a "move towards" person. She deals with anxiety and conflict by moving TOWARDS the person, trying to console, ingratiate, and get on their good side. Someone who Moved Against or Moved Away would do better with stalkers... but her natural skill and instinct is to negotiate with people so that everyone is happy and they are no longer displeased with her. Where she is weak is that she's not willing to live with anxiety that she sometimes must suffer is she is to protect herself.
It might gall you that she is not acting as independently as you would like, but I think she's going to need more support than you'd expect. And to be taken care of, to some degree. Guys like you to get involved and get rid of this guy. Even if she should be developing more independence, she can't do enough of it to save her from this creep.
I would probably try to keep convincing her that this guy is NOT part of her social circle, she has no commitments or obligations to him, he is crossing her boundaries, and thus she needs to see him as an interloper and someone she can truly "lock out" rather than trying to engage, placate, salve, or maintain a relationship with. Even that it's better for her to feel harsh, cruel, evil, or mean than to keep allowing him to violate her boundaries. She might need to support to just let her know she's not any of those things for cutting him out.
I don't know, obviously you know her so much better so perhaps my advice is off a great deal. But I would not hesitate to step in, in this situation, and help her "take care of this problem." Some people just need that level of support, even if we would not.