C.P.
I don't really have a solution for you, but we had the same issues around the same time with our son. By the time he was 8-9 months old, I was so sleep deprived that I was willing to try just about anything. We even had issues at night time and during the night... not just napping. At that age, we used the Ferber method and within a few days, it worked AT NIGHT. We were never able to get him to fall asleep on his own for naps at that age. But I recommend reading Ferber's book "solve your child's sleep problems" (the newest edition)... his method is like crying it out but you'll go in and check on baby every so many minutes at longer and longer intervals...
another suggestion is to make sure that you have room darkening blinds/curtains/whatever on windows in baby's room. this makes a HUGE difference, especiallly in summer when it's so bright out.
just to make you feel better, our son never napped more than 30 minutes at a time until he was about 11-12 months old, and then it gradually turned into an hour, then longer and longer.
is your baby getting enough physical activity while awake? plenty of tummy and crawling around time, if she's not cruising or walking yet? if she's not tired, she's not going to want to fall asleep. also, get her outside as much as possible during the day. fresh air works wonders.
hope this helps
hang in there... it will get better
I also recommend reading "the no cry sleep solution"....
The Ferber method stopped working for us once our son was 1 year old... this book was a life saver! I have the toddler version, but I'm sure either would be useful... lots of great ideas...