This looks very suspect to me. The portion on her tail may be retained shed, but the area around her vent (which is a bad sign, it's where Yellow Fungus tends to start) looks very much like Yellow Fungus to me.
Yellow Fungus grows both internally and externally, which is why it's so incredibly difficult to treat, and absolutely requires a prescription for the oral Antifungal medication Voricozanole (the drug people seem to have the most luck with), along with a prescription topical Antifungal treatment as well. This is one of the reasons they think it typically grows around the outside of the vent area, as it's spreading from internal to external surfaces.
The key to even having a chance to treat Yellow Fungus successfully is getting a Skin Scraping test taken and sent in ASAP, and if it is determined to be Yellow Fungus, getting them started on the daily oral Antifungal meds immediately, before it overtakes their entire internal viscera. So you need to get her to an experienced Reptile Vet with Bearded Dragon experience/expertise immediately, because the test has to be sent out and will take a week or so to get the results.
Petco does not have a "store veterinarian" at any location like PetSmart does (they own "Banfield Veterinary" and have offices built inside certain Petsmart locations), but rather Petco has a mobile vet service that will come to the location. However, some locations don't even have this, they actually will send the pet to the closest local vet that "is willing to see" a reptile. Usually this means either a general vet or an "exotics" vet that knows nothing about Bearded Dragons. However, any vet can take a Skin Scraping sample and send it out to whatever lab they use for testing.
Once the test result comes back the hard part comes, because treating Yellow Fungus usually involves 6 months to a year minimum of a daily dose of Voricozanole along with prescription external treatments to even have a shot at getting rid of the Yellow Fungus. So Petco will probably opt to just euthanize her and give you your money back or another baby dragon. However, THE PETCO YOU JUST GOT HER FROM NEEDS TO BE NOTIFIED IMMEDIATELY ABOUT HER POSSIBLE DIAGNOSIS OF YELLOW FUNGUS, IF YOU HAVEN'T ALREADY DONE SO, AT LEAST CALL THEM IMMEDIATELY TO TELL THEM, BEFORE THEY SELL THE OTHER BABY DRAGONS SHE WAS HOUSED WITH, AS YELLOW FUNGUS IS EXTREMELY CONTAGIOUS, AND ALL DRAGONS THAT SHE WAS HOUSED WITH CERTAINLY HAVE IT, ALONG WITH OTHER REPTILES IN THAT PARTICULAR STORE.