Well... it's a tricky one considering Carmela's touchyness about schedules. i'd say to play it by ear, that is, make her bedtime when she seems tired. If it's at usual bedtime, then go with it. If it's at 8, then switch her bedtime. Also, as i know you've been struggling with her about naps lately, how would you feel about only tweaking the schedules on days she goes to preschool? Since it's only 2 days a week and she seems to finally have settled with her current routine, why not tweak this one as less as possible? just a thought, of course you know her better and will decide in terms of what's best for the whole household. Anyways, we'll be here for you!
Good luck and congrats on carmela being such a big girl!