I can't remember...was this girl a friend of a friend or relative or something? I wouldn't waste any more of your time with her. I would talk to her or e-mail her or however you've been communicating and say thank her for her interest and give her 3-5 final choices for $100. Maybe stacked 10 and 8" made with straight cake mixes and standard crusting BC.
You've probably already done all of this, though.
10 and 8" should be enough for 60 and they should only take a few cake mixes.
Anyway, I would give her the choices and say that is it. THat's all you can do. Give her a deadline to get back to you (like 24 hours) with her decision, no matter what that decision may be, and hold her to it.
Honestly, though, I would forget the whole thing, unless she is related somehow or a friend of a good friend or relative. It's just not worth it!
BTW, I have not really sold any cakes, so I am way out of my league here...just offering my 2 cents.