First off, this seems to me a natural time for your daughter to be exploring boundaries. Your 8 month old is probably starting to understand who you are and naturally just wants to spend as much time awake with you as possible!
We encountered a similar situation with my son around the same age. The following worked for him and for us. He is a great sleeper, it's better for him to be rested, and better for us that he's not running us ragged with hours and hours of trying to get to sleep.
I have some friends who have tried different approaches and their kids are not good sleepers or else sleep with them all the time, which is harder and harder to break as they get older.
Set a routine: 2 naps and bedtime. I read the Dr Weissbluth (sp?) book and my one takeaway is that kids that age don't need to be up for more than 2-3 hours at a time. Don't let your child get overtired or they'll have more problems falling asleep. They can become overstimulated and are too tired to soothe themselves. So set a schedule and keep it (of course with some flexibility). Watch your daughter for signs of being tired and put her down BEFORE she gets overtired.
Make sure you follow your wind down routine (sounds like you have a great one) before each sleep period. Our wind down takes about 5 minutes in his room (music, shade down, diaper, rock and read a book). Then put her down and WALK AWAY - even if she's crying. I know that sounds rough - harder on the parents than the child, I think. You probably know your child's different types of cries at this point - so ONLY go back in the room when something is 'wrong' - diaper, food, but really you probably take care of all of that when you're in your wind down routine.
Whatever you do - don't keep walking in and out of the room, or picking her up and putting her down - just let her work it out. She'll come to understand very quickly that it's sleep time and she can let go and relax.
I really don't think this is cruel: you want your child to learn how to soothe themselves and fall asleep. You've made sure they're safe and fed and clean, and had cuddles with them, so don't believe it's harmful or neglectful to set a firm bedtime.
This approach was very hard for me the first day, but my husband encouraged me to stick with it, and boy am I glad he did! Within about 3 days, our soon got the routine and has been a great sleeper ever since.
There are of course days when he does get overtired, that's life, right? We just allow a little more wind-down (reading, etc), then let him cry it out. It's usually less than 5 minutes before he's sound asleep. He's 16 months now.
Sorry this was long-winded. I'm not very opinionated on many parenting things, but this is one I feel strongly about!
Good luck with whatever approach you take!