Should a dog be on life support?

If it were my dog, I would have it put down. There is no reason an animal should suffer. I don't know if there is a medication to keep the dog from having more siezures, but it would only be fair to your sister to find out. If she is responsible enough to do so. But seriously, if you could talk her into putting the dog down, it would be best. I know it is hard to lose your pet. But I would rather them be dead than not suffer. Good luck with your sister. Maybe if you did go with her, you might be able to talk to the vet and have the vet tell your sister what really needs to be done.