Started to avoid food in heat

so I have a 1 year 4 months shihtzu and she has been in heat for about 2 weeks now, yesterday we went to the vet to get her annual vaccine of rabies and all those diseases but since we came back she has not been eating anything She was loving her food just one day before but now she hasn't eaten anything a whole day Is this normal? She did eat some yogurt only after about 2 hrs when we came from the vet