Hi there...it is quite common for cats to become sluggish for a couple days after receiving vaccinations. Additionally, the stress of visiting a strange place is exhausting as well. Please keep a close watch on her to make sure she is still eating and drinking (even a little amounts). If the symptoms persist beyond 2 days please contact your vet or if there are any questions consider ringing your vet to understand the post vaccination effects.
Vaccinations and side post effects by Dr. Christianne Schelling (see very last paragraph): http://www.catvaccines.com/feline_vaccination_guidelines.htm
Vaccine reactions can occur and range in severity. Mild general lethargy and injection site soreness are not uncommon. Immediate vaccine induced allergic reactions can also occur. With these types of reactions the animal can have vomiting, diarrhea, facial swelling, and other signs of shock and must be treated immediately by a veterinarian. Although vaccine reactions are frightening to the owner, other than the vaccine-induced sarcomas, they are rarely serious or life threatening. In almost all instances, the benefit of vaccination far outweighs the risk of any vaccine reaction.