Thanks for the good thoughts everyone!
I'll keep the possibility of fungal infection in mind if she ends up going back in on Monday.
I don't know if Oreo has had a heartworm test recently, but since she had accompanying nasal discharge and coughed up mucous several times (as well as being on Interceptor), i think that heartworm disease is a pretty small possibility. My dad did say her heart's fine, so it sounds like they may have had a good listen to it as well.
Do you know if slippery elm is ok for an animal who has had seizures (and many at that) in the past?
Erin, the Amazing Maggie Mae, and Super Puppy Ziva