The more consistent you are with bedtime, the better because otherwise it can really throw things off. That said, if your lo is tired at 6:30 PM, you gotta do what you gotta do. Just go ahead and put her to bed - don't make her wait another hour. (Doesn't she wake up an hour ealier, though?)
If you can work on the naps during the day, making those a bit more consistent in terms of length, that should make bedtime more consistent (easier said than done, I know, but that's how it works :?).