I used to work in fundraising, and I see a lot of parallels- it takes people skills, selling a product (whether it's your cause, or yourself), and ultimately, convincing and getting people to do what you both want them to do.

We were told (and it's totally true in both the fundraising and pickup worlds) that around 10% of people will flat-out 'buy what you're selling' with no questions asked, 10% will not go along with it, under any circumstances, and 80% will take some work, and will go along with you if you play your cards right.

Oftentimes, I'd come across someone who wanted to contribute, but had it in the back of their mind that they shouldn't be giving money to someone they just met, and would say, "I'd really like to, but _______", and give an excuse I'd never heard, and didn't have a planned response to (ie, LMR.) My response to this was (here's your TLDR) "Well, I can't make you do something you don't want to do." This set up a reminder in their brain that they'd already said it was something they wanted to do (this could be anything), and reinforced that they said they wanted to do it, which often got the results I (we both) wanted.

Note, this only works if (A) they've said they "want to, but ___" and (B) you've developed a strong connection with them. If it's one of the first things you say to the girl, she's much more likely to blow off the comment as you giving up.

Edit: As with everything, say it in a teasing, confident way, as if you both know what she really wants to do (because you do...). Don't say it in a desperate, helpless way. The phrase already implies being desperate and helpless, but I use it in a sarcastic way.

This might seem a little manipulative to some, but I see it as a convincing reminder, to get someone to do something they've told you they want to do.