"would you mind leaving me some feedback on our recent transaction?
Believe it or not, she could report you for spamming her if that is the only reason you would be writing. While it might be that she doesn't know about feedback, doesn't feel like leaving it, she may want to wait and leave it for several at a time.
To lower the risk that she might find you to be a pain and report you..if you are going to write her anyway, I would just say.."since you are fairly new, I wanted to make sure you checked out the feedback I left..I know it's always a thrill when a new eBay user gets feedback. If you are so inclined, I would appreciate feedback being left for me. Thanks"
If I get an email that the item has arrived, I used to let them thank them for letting me know, and let them know I'm off to leave positive feedback, now that I know the item arrived safely (although my feedback is now automatically left through Vrane, so I no longer do this) and let them know I would appreciate feedback being left for me.
However, I have to say, that it might be best to just skip this. I know one gal on another eBay board who leaves the following when asked to leave feedback (she leaves a positive)..
There..happy? She asked, so I left feedback.
Is it rude? I think so, but maybe this person doesn't want to leave feedback at this time.