Poo sticking happens all the time. (Especially when grandma visits and sneaks her some table food.)
If you're trimming with scissors, invest in a small round tipped pair. You don't want to cut anything down there.
Also, just remember:
When the poo gets stuck to the rump, pick her up ** rear-end facing away from your body ** & just carry her straight to an empty sink. If you have a nozzle sprayer, just spray the hind quarters. It all comes off. Even if she hates bath time, she'll probably be glad you rinsed her.
Good luck.