In a romantic relationship, I tend to let people in just a little bit further & the "safety chain" thing probably refers to the little tests we INFJ's give to people we are interested in. I'll throw some things out there hinting at what's behind the door in order to judge the reaction of the person. If I get a negative one, the door won't be opened.
It may be that she's scared of being hurt, but there's nothing you can do to *help* her. It's not something that she needs help with or something that is even wrong! If you go the route of helping her, you may cause some resentment. I had a boyfriend once who tried to "save" me from what he perceived to be my insecurities & fears, but I never undersood what he was trying to save me from - as I was just being myself. Maybe at the core of my existence, I open doors one at a time because I'm scared of being hurt - but I also do it because that's who I am and my private life is something I only choose to share with those whom I trust fully. I just don't feel comfortable sharing it with everyone I meet - nor do I desire to do so.
The whole opening door thing is also how I keep acquaintances or keep people in my life that I do not consider close friends. I have perfectly healthy relationships with these people because I keep them at the door I choose. To compare this to an ENFP, I noticed that my best friend will discredit someone COMPLETELY if they do something against her personal value system (and take it very personally). I'll just not let that person get past most of my doors.