Hi B.,
Generally, babies at this age need about 14 hours of sleep which comprises of 10-12 hours of sleep plus two 1-2 hour naps a day. Usually around 8-10 months, they start to become more aware and have more separation anxiety, making bedtime a struggle. My son went through this exact thing and it started carrying into the naps as well. We rocked, tried music, etc and it was very difficult. The only thing that worked was to let him cry himself to sleep per the pediatrician's advice. Only then, will they learn to comfort themselves. It's not easy, but it works and you get through it. I now put a book and a few soft toys in his bed for him to look at until he falls asleep.
The other possibility is that she may be cutting teeth. You can lube her up with Hurricane gel (available behind the pharmacy counter; 20% Lidocaine) or Motrin if she really acts like she's in pain. However, if she's fine when playing and then starts fighting bedtime, you can be pretty sure she's not in pain.
Lastly, another factor may be that it gets darker later, which may not allow her body to produce Melatonin (sleep hormone) until later. Darkness prompts the body to start producing it which induces sleep.
Use process of elimination and then, when all else fails, let her put herself to sleep.