Hi E.,
I think that you should continue putting your daughter down at the same times that you always have if she still seems tired at those times. When she cries, just do the same things you do at night (check diaper, etc.) and then do the 5-10-15 minute checks. Come back after 5 minutes of crying, tell her you love her and that naptime will be nice, sweet dreams (without picking her up though!). If she continues crying, go back after 10 minutes, then 15. Go up to 20 minutes between visits. After a while if she's really tired she'll sleep.
As someone suggested, if she's teething that could be why she's having a harder time, but that is also something you'll notice in her waking hours. She'll chew and gnaw on things constantly, have her fists in her mouth, drool, etc. It won't be something to be attributed only at sleepy time.
Kids go through sleeping phases during the day just like they do for the nighttime rest, but that doesn't mean they don't need it. Generally kids don't outgrow naps until age 3-4. Good luck!