You mentioned you're worried about your ability to communicate, but it seems to me that you've expressed yourself pretty well here. This may sound a bit trite, but maybe you could write her a letter? I know people sometimes make a big deal about discussing these things in person, but if you just told her "There's something important I want to talk to you about, but I'm nervous that I'll have a hard time expressing myself or forget everything I want to say, so I wrote it down," to me that would seem really thoughtful. Decide if you want her to read it then or read it in private, or give her the option, depending on what you're comfortable with. Then you can have an in-person conversation following that.
Otherwise, I agree you should just talk to her about it. It'll be better to know than not know, even if it's scary. You say you're worried about stepping over a line or being insensitive, but nothing about what you've said here sounds that way to me. You sound like you really care deeply about her and have a lot of respect for her.
Good luck!