Hi J.-
Sleep needs shift as they get older, and I found that the transitions (from 3 naps to 2, then 2 to 1) can be tricky. She's probably ready to give up that 3rd nap, but it usually doesn't happen overnight. When my kids did 2 naps it was around 9:30am and 2:30pm, each about 1 1/2 hours. If she's getting up at 6am, 9:30 can be a long time before nap (lots of babies will want to nap about an hour after they wake up)-- so you'll have to try to keep her up, and stretch that time later into the morning each day until you're on the routine. You may want to try to pull her bedtime back more to 7 or 7:30pm too, so she can sleep a little later in the mornning. In the beginning, you might have a cranky/overtired baby, but she should adjust within a week or two.
It's hard to tell about teething, isn't it? But, if she's waking up and wanting to play, or is immediately comforted if you pick her up, she's probably not in pain.
Good luck!