well - 1st take into account that you were out of the house visiting - busier than usual? noisier? more playing with her / holding her / being in her face= overstimulation. and then if she was not sleeping in her usual environment = also affects it.
honestly if you are trying to get longer naps and she does not do well outside home for sleep then it was never gonna happen at your parents no matter what. if you have days that are "extra" anything (lots of errands, family gatherings, parties etc) you need to take those into account when planning her A time. so just as if she has a short nap your instinct is to compensate by bringing bedtime forward a bit, you need to look at her days the same way - so for illness you adapt, for teething, parties etc .... you have to be flexible and adapt the routine to suit her needs and your lifestyle. It isn't something solid where you take 6 hrs and run with it IYKWIM, it is still something fluid that requires your tweaking since you are there with her every day.
good luck with bedtime. tomorrow is another day.