Sometimes if it takes multiple sticks before an LP is successful, you can have inflammation of the area. Making sure she's hydrated and taking an anti-inflammatory can help. Best choice is to call the doctor to discuss (as you say will happen tomorrow). I've also heard sitting for extended periods of time can make things worse so it's better to make sure to do some "soft stretching" every couple of hours if she has to sit a lot.
Again, please contact the doctor to get the best advice. Viral Meningitis is a serious diagnosis and I would be in very close contact with her doc (or she should be if she's an adult). Nothing to fool around with.