Hi Mindy
I am probably not the best person to give advice as we gave up on pu/pd the second time round after illness (just us being lazy, not our LO!), but it did work the first time we did it.
Anyway, what we ended up doing when our LO was your LO's age was just put them down wherever we were out and then transfer her into the car and put her to bed when we got home in the usual way (we put her in her pj's when we were out). Many times she never woke up at all.
I think that letting her fall asleep in her pram from time to time will not spoil what you are doing as long as you remain consistent at all other times.
Nowadays (LO is 20 months old), if we are out in the evening, we don't have a chance of getting her to go to sleep if we will be going home, as everything is just too exciting for her, so what we do now is arrive and leave earlier than we might have done otherwise, and get her ready for bed before going in the car, so that we can just put her to bed when we get home. If it is something really important, we let her nap for as long as possible in the afternoon and just keep her up at the outing till she can handle it (say, 9 or 9.30pm at the latest), then get her routine back on track the next day - easier to achieve with an older one, though, I think!