to throw my hat in the ring here...
i actually have been in a similar situation. I have this to say about it. If you've told her before, and she's not a complete moron, odds are she already knows that you want it/need it/love it. So, as genuinegirly more or less said, or else as I'm saying, you may be better off not asking her anymore. I actually went this route - stop asking all the time, apologize, say it's inappropriate to ask all the time, but you know that it is one of my favorite things ever so now and forever, konw that i am 100% interested in it. something along those lines. She thought it was very touching and loving and communicative and everything. and I started getting them more regularly. Everybody wins
