Hello. Thanks for the question.
Seizures in cats can be tough to diagnose. In dogs, it's most likely due to epilepsy in young animals. In cats, epilepsy is less common. In cats, it's often due to an organ disease (kidney or liver), toxins or a structural disease in the brain (tumor, clot, bleed).
The best test is an MRI of the head. I don't recommend that right away, but if any further seizures are seen I would consider it. This is done with a veterinary neurologist. It's expensive, but it'll give you an answer as to the cause. They also typically do a CSF (spinal fluid) tap at the same time to rule out meningitis or other infectious causes.
For now, I would just monitor her for further seizures. I don't usually recommend an exam or emergency treatment unless they have more than 2 seizures in a short period (cluster seizures) or a seizure lasting more than 5 minutes (status epilepticus).
Here is a nice write up on seizures in companion animals:
I hope this helps, let me know if you have any other questions.