Are you on a typical 4h EASY with 2h A time and 2x2h naps and a catnap? Before you started PUPD was she settling and sleeping without a problem?
5-6 months is a typical time for routine to go haywire, as babies often need more A time and a move towards the 3-2 nap transition. It could be if she got good naps in the day she was UT for bedtime, so fought you, or it could be if her naps were more disturbed than usual that she was OT and struggled to settle. I wouldn't change things on the basis of one day usually - could you perhaps note down what happens over the next couple of days and then we can see if there's any sort of pattern emerging?
Personally I would keep going with PUPD for naps and bedtime as that gives her more chance to practise