D., I am going thru the exact same thing with my dd (14.5 months) right now. My dd is taking FOREVER to fall asleep for her naps and sometimes just won't do it. We call it 'rest/quiet time' and if she doesn't sleep after an hour or so, I'll just get her out of the crib. Good thing is she doesn't cry, just plays and talks.
She's an early riser, 6am most days. So, by 9ish, she's fussy and tired again, even though when I put her down she doesn't fall asleep right away or quickly. I don't get it!!! LOL! Most days, she will fall asleep by 9:30 and sleep till 11. I have thought of only letting her go an hour so that she will take her pm nap more easily. Some days it works, other days it doesn't. Some times I feel bad about waking her and that I should let her sleep, but I really don't know.
I have tried one nap a day for a few days, but it's totally random. The first day she slept 11:30-2:30. I was like 'awesome!'. But nope. The next day, I did the same thing and she only slept 1.5 hours and then wasn't tired till about 4 and I didn't want to let her nap then b/c normal bedtime is around 7-7:15.
I like pp's suggestion about taking her out at 9am (even though she's showing signs of being tired) and running errands or playdates or whatever. Just something totally different than what she's use to. It might work out! Then if I could get her lunch by 11 and then nap at 11:30 and bed by 6:45-7. This is something that I've been thinking about for a week or so and just haven't acted on it.
Oh, I also read recently that it can take them a little while to get use to napping 2-3 hours straight. So, hang in there! We'll get it worked out soon! Good luck.