Many dogs in this situation will refuse food. I had a new foster who ate Scooby Snacks (don't judge me!) for quite a few days (and nothing else) until she could calm down and settle in. I would probably start trying to transition her from that food anyway, so that's good that she's refusing it.
With most foster dogs I will use something like Merrick canned food, a couple of tablespoons, mixed with water and kibble and that seems to kick up the appetite. If I need to I will do other things to stimulate the appetite. Warm homemade food like meat and sweet potatoes, baby food, more canned than dry, are all things I've tried as I get more concerned.
If she's drinking water, I would be happy. If she's not doing that/refusing water, then I would be very nervous.
It is always possible when getting a dog that they bring with them parasites and worms, so taking a fecal in, and getting a heartworm and tick test is always a good idea. Take any old vet records/shot records with you. Unless she's not had a rabies shot, I would hold off on shots for another visit and not combine rabies with any others if they are needed.
Way down the road if she still continues to be picky, have a very low weight (can't tell from the pic other than that she's very pretty) and loose stools you would want to test for SIBO/ARD and EPI. But that's a long way off in terms of what you are likely seeing.
Good luck and welcome to the board!
ETA - I do a 2 week shutdown to help dogs relax in their new surroundings - you can find it online - I have modified it for myself but pretty much trying to prevent a dog from being overwhelmed and it helps them to resume eating better.