It can be both (a father figure fixation and a crush) Her behavior sounds flirtatious and her disclosing things about her life indicative of poor boundaries.
From the post is not clear what the age difference is and if the two of you are dating or are coworkers etc. You may want to pay attention of who she treats other men who are older than her.
Depending on how you feel about this, you could approach her and try see what her intentions are and get your answer so to speak "straight from the horse's mouth".
If you are not interested in pursuing a relationship, you may want to let her know earlier rather than later.
She is 20 years junior to me. She tends to rub against me and leans closer when I talk. I have noticed that she treats only me this way. She does not like other women looking at me, not dating. She also does anything I ask her to do. Has sent me cards saying " how much I mean to her in her world" and I have stolen her heart. I care for her, but don't want to ruin the way it is now by confronting her. I'm a little confused is all.
You have a valid concern. Her behavior is quite flirtatious (yet it would be good to be cautious about a female making the first moves in such an open and possessive way)
What would my concerns be if I let it go on? I love this girl.