Ok, the signs you are describing are quite vague.
The vacant staring episdoes, along with the restlessness, can be pre-ictal signs, which may indicate a partial seizure. Not a full epileptic seizure but a milder form. This can be an indicator of an underlying neurological problem. In epileptic patients, females can often be more likely to have a seizure around the time of heat, and this pattern would certainly fit with the signs you are describing.
In some instances a urinary tract infection can be associated with neurological signs, hence I was asking about her thirst and urination.
Diabetes, an uncontrolled blood sugar level can also be associated with vacant, restless episodes, so this would be something to exclude.
The restlessness can be a sign of discomfort, so changes in the way she walks or reluctance to jump up, poor balance etc could be indicators of back pain.
There are many possibilities here, and I feel only a thorough clinical exam will be able to rule many of these things in or out.