[Ellie May]

I think I'd be switching vets.

That is not at all normal procedure.
Ellie had a severe reaction to her vaccines once and the one that most likely caused it (lepto) is now left out. She has only gotten one distemper single since then. She got a shot of benadryl and 15 minutes later was given the vaccine. We also waited about 30 minutes after together in the waiting room to make sure all was well.

I wouldn't be convinced your pup needs an IV at all.
If they want to give benadryl before and/or watch her for awhile after, you could stay for that in my opinion.