I don't know that you necessarily need another opinion. From your description, your veterinarians statements are sound. Epilepsy can be defined in a couple of ways but in general 'epilepsy' is going to start 6 months to 5-7 years of age. With facial and body twitching the brain or upper (proximal) spinal cord lesion is likely. I agree that a tumor may be a cause. Infection and inflammatory causes may also be the underlying cause. MRI and CSF tap are the definitive diagnostic tests. While I believe that blood tests are important, I agree with your veterinarian's statement.
I have a couple of thoughts on her, assuming that these tests cannot be afforded. First you can video record these episodes and have a consultation with a neurologist. Occasionally there may be signs which are pathognomonic for a particular disease. Another thought would be a therapeutic medical trials of medications like antimicrobials, phenobarbitol and/or steroids. None of these are of course as good as a MRI but I hate to give up an anyone! Some patients can really positively respond to empirical medication administration.
Also, are you in an area or has she ever been in an area of fungal infections like valley fever (coccidiomycosis) etc... Perhaps ask your vet. Some fungal infections can set in the brain and can be treated or managed well.