Much like people, some horses are just more aloof than others. Some horses see "their human" and give a whinny and try to crawl into his/her lap for attention, others look up and then right back down to their food. It's an individual thing. As long as she's respectful and obedient, I wouldn't be too concerned.
Some groundwork type exercises, done correctly, certainly can't hurt. It's mostly a time thing - spend time with her, she'll get used to that. If you can logistically do it (not sure if you're boarding, etc.) try to be the one to feed/care for her every day. If it is a trust issue, and not simply an aloof personality, that will go a long way to getting her to "open up". You might look up some TTouch exercises - I don't put a lot of stock in it as a "training miracle" or anything, but my guys certainly enjoy the "massage" every now and again. One other thing to try is to gently breathe into her nose. That equates to "formally introducing yourself" in horse-ese; note that in a herd setting, horses will greet one another this way. Just be with her, doing things, both actively (groundwork, riding, training) and more passively (feeding/grooming, TTouch, hand grazing).
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown