Hi, welcome to Yorkie Talk. Glad your furbaby got help and is doing better
Definatly let your regular vet know before the vaccine booster. What specifically was in the distemper shot? It's a combo. vaccine - does the paperwork say DHPP or DHLPP? If there's an "L" in there, tell your vet you DO NOT want Lepto vaccine anymore, but I'm sure if you explain her reaction and it was used, they'll come to that conclusion. Another thing you can talk to your vet about for next time is possibly giving something like Benadryl prior to getting vaccinated.
(just a side note - you should think about switching to a different food, Iams isn't good, it's full of corn and byproducts)