My daughter started doing this to me at 10 months. Part of it was teeth. 2 times we found out she had a double ear infection. Does she pull at her ears or anything that may indicate an ear ifection? This is a possibility. When Stevie's ear infections were cleared up, she just wanted to be up w/me, plus once she learned to stand in her crib....well that was it, I'd lay her down, she'd stand up! Anyway, I know alot of moms don't like to do this but I think it works, and I've done it w/all my kids. If you've given her some motrin and time enough for it to kick in so hopefully her teeth aren't hurting her too much, I do the cry it out theory. I know, I know, you feel horrible doing it, I know I did, but you have to let her know it's nap time. It took a good week or 2 for me before Stevie got the idea but she did. I would put her down, give her a kiss, say I love you and leave. She'd obviously cry...scream her brains out was more like it. I'd let her cry for 10 minutes and then go back, give her a hug, reasure her I was here and tell her it was nap time. At first I had to do this for about a 1/2 hour. 1/2 hour was my limit, had she continued I'd have let her get up. But she didn't, she fell asleep and each day it would take less and less time for her to fall asleep. Now she may give me a boo-boo face when I say goodnight but once I leave she's down. Or she may cry fora couple minutes but she goes to sleep then. My husband HATED me doing this. It broke his heart to hear her cry, and the evil looks he gave me...my goodness! In the end tho, he told me I was right. Babies and kids need to realize you're the boss. When you start letting them pick when and IF they take naps or go to bed you're only letting them be in control. This is all my opinion and I know others think differently and this may not be what you want to do, but it's a suggestion.
S.