E.B.
We are going through the same teething issues with our 17 month old. He's actually working on his 2 year molars. He's been miserable every other month since Christmas and so have we. Recently, I started being more aggressive with the pain meds and it's really making a difference.
First, you can't overdose her as long as you don't exceed the daily recommended dosage, and it's safe to give over long periods of time. What I've been doing is giving 1 tsp of Motrin with breakfast, then about an hour and a half later, I give 1.6 ml of Tylenol. Make sure you adjust the dosages for your daughter's weight, of course. Then I continue the Tylenol every 4 hours (usually two more times during the day) and then finish up with another dose of Motrin about a half hour before bed. It's ok if the two meds overlap - you won't "overdose" her because they're different medicines. My theory is that the Motrin will "kickstart" her day, then the Tylenol offers more consistent relief because you can give it more often. Then at bedtime, the stronger Motrin will help her relax and fall asleep.
Doing this has completely changed everything for us. Our son is like a different person - yesterday in the grocery store, he just sang and flirted with other shoppers. I've normally had to give him snacks, binky, cell phone, etc. just to stop him from whining. He's sleeping a lot better too. Try this, it worked wonders for us!