Briefly, she could have been spay
and bleed. Do you think she was in Season
and, if so, how far along? If she was in Season and they mated, she could be pregnant or just refusing the male. Sometimes, you can get an indication of a pregnancy. Some females will go off their food. Some will have a type of morning sickness and get sick to their stomach.
I have always checked the vulva area. If she is done with her season, check to see if the vulva is swollen and soft.