cheekymonk - it does sound like it is nap related & she is cutting back on her daytime sleep needs. Glad you are having some success with cutting her nap back a bit. We never managed to do that successfully, ds was always a horrendous grump if woken from a nap earlier than 2hrs!!!
One thing I've come to accept with my ds since he turned 2 is that on days he naps there is absolutely no point in putting him to bed before 8pm because he simply isn't tired enough. So we have 2 routines - on nap days he will nap approx 2-4pm & bedtime is 8pm, if he has no nap he's usually in bed around 6.30pm. By putting him down later on nap days, there is no messing around, its straight to bed & he's usually asleep within 10mins.
Another thing I have found with him, is the earlier in the day he naps, the more messing around we get at bedtime. So if he were up at 7am & napped 12-2, he would arse around for aaages at bedtime, whereas putting him down 2-4pm means he's had a much more tiring morning & is way easier to settle at bedtime.
Finally, wrt her constantly getting out, it may have become a bit of a game for her, by you staying in the room & continually putting her back in. I am wondering if perhaps the antics continue even with the shorter nap, it would be worth putting up a stairgate & then putting her to bed once & then come straight out & leave her to it.
If my ds is reluctant to get in bed I usually just tell him calmly & firmly that it is time for bed now & mummy is leaving the room & then I give him the choice: he can either get into bed & I will tuck him in or he can stay on the floor & get in by himself in the dark. It usually does the trick 
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Failing that, perhaps a reward chart for staying in bed with a treat if she achieves say 5 good bedtimes? hth.x