Like always with me, I can't really say how all ISFJ's would act, only how I would act, and hopefully it will be accurate for her as well.
First off, your description of her does make her sound like an ISFJ, so it looks like you're on the right track.
For me...my friends are those that I feel very comfortable around. When I'm around people that I'm not comfortable with, I get very quiet and awkward, not wanting to say anything, and kind of wanting to leave.
But with my friends, I feel like I can be myself. I can make goofy jokes and not worry about them not being funny or people thinking that I'm just stupid. I can share my feelings and not feel like I'm going to be judged or feel like it's going to come across as weird. I can just relax and be happy.
It's good that you say you're a strong feeler, because that's where I think ISFJ's and INFP's can really connect, when they feel comfortable sharing their feelings. So if you ever experience any one on one conversations with her where she's sharing things about herself or talking about her feelings, that's a sign that she trusts you and views you as a good friend.
If you're looking for ways to help build the friendship, the key thing is always showing support and never judging. You can ask her questions about anything about her to show interest, and whatever she's chooses to tell you, be very careful that you don't make fun of her or think it's stupid or anything like that. Once I get a hint of someone feeling that way about me, I tend to shut them out, not trust them, and not view them as much of a friend.
Of course, once I get really really close with someone, I don't mind them making fun of me in playful ways or judging me. But that's because I have
strong confidence that that person accepts me and is really my friend...I have full confidence they're just having fun and don't mean anything by that. But until I get to that point with someone, those kinds of things can make me shut them out.
The only other thing is...don't worry if she needs some time alone or won't talk. If you ask her questions and she gives short answers or appears disinterested, it may just be that she feels like being alone at that particular time. It's usually not personal. It's only personal if you've judged her or done something to make her feel bad, as I mentioned in the last few paragraphs. But, if you haven't done anything like that, don't worry if she doesn't open up or share...she may just not feel like it at the time. So just stay patient...a lot of times it's about her, not you, if she's not opening up.
Again, I really can't speak for her, only me. I think I'm just very wary about opening up to people because I'm afraid of being hurt. So as a result, I only have a few true friends, but those friends I do have I trust very deeply. So I don't know how similar she is to me, but hopefully this helps you somehow!
