Rescue Pooch Has Not Pooped?

Yesterday my rescue dog Gracie arrived at 13:40. She's a smooth haired Collie almost 4 years old. My concern is that, so far, she hasn't pooped and has only peed once, this morning at 7:15. She didn't attempt any toilet functions on her walk last night. I have a garden and the door is open, because of the good weather, but even though if she needs to go she can, she isn't if that makes sense.

She ate perfectly well this morning, but no poop and she's not remotely interested in the fish or liver treats I offered her this afternoon as a reward for being in the garden. I thought encouraging her into the garden may help, but so far nothing. I don't want to overreact, but nor do I want to ignore it if it is a problem. I've only had puppies before so have never come across this issue with an adult dog. She definitely isn't doing the 'business' elsewhere so should I simply go straight to the vet? Any nuggets of wisdom greatly appreciated.
Thank you.