You're learning. Good.
Now. Here are a few things you should do. First, stop with the IM'ing. I know everyone seems to be in the digital age, but nothing works better to convey subtle messages than inflections in a voice over a telephone, except, of course (and it's spelled "course" not "coarse") a face-to-face meeting where your eyes and facial expression tell the story.
Second, your "I hate to be picky" was a good move, as it exposed her insecurities about you. She obviously wants you in her life, and she thought you were about to say something negative about her that is affecting (if not terminating) your desire to occupy that position. Yet I'm not sure that she wants you in her life as an exclusive boyfriend/lover/husband, etc...just yet. As you indicated, she's a senior in colllege. She's just getting out of the best years of her life, when her looks and charm were paramount for getting what she wanted and for having a good time. She's about to enter the big bad real world -- a place you already are -- and she's scared. Consequently, your being a part of her life provides a degree of reassurance that: (a) her looks and charm can work on non-college guys; (b) she has a safety net/shoulder to cry on/guide in the wilderness if the transition to the real world gets too tough (perhaps even as a father-figure); and (c) you provide bragging material for her to her friends.
Third, you need to pull back, and force her to temper her enthusiasm as the carefree college graduate with the thought that the experiences associated with her desire to have fun would be so much more interesting if shared with you, rather than still-clueless college graduate guys. You bring far more the the table than they do, and as long as you convey the message that you're not trying to tie her down/clip her wings (which you appeared to be doing, which is why she backed off), she'll stick with you. However, throughout the process you need to restrain your feelings for her -- there's nothing wrong with them -- but you need to control them, not the other way around. Trust me, you, and hopefully your relationship with her, will be better served by doing so.
Finally, I'm glad my suggestion that you would have invited her to come along, but you thought she'd be too busy, worked well for you. It often does when a woman is trying the "old friend from out of town" or other type of pull back game. Going forward, she'll start initiating again, but be on the lookout for hints in her voice, expressions, etc... that indicates she wants you to invite her along on your next night out (by the way, women LOVE casinos -- it projects an image of being a high roller, James Bond-type sophistication). Adventures such as casino gambling, boating (especially sailboating), wineries, private tours of museums, gallery openings, etc...would make any recently-graduated college woman weak in the knees. They often dream of these types of adventures, which college guys could never give them. Once they've graduated, women don't want to hang out in bars all the time shooting pool.
that can persuade her without her even knowing it that she wants to be with me, and start this new part of her life dating a somewhat older guy. Its not gonna be a cakewalk that is for sure. 
