Benadryl can help, but one is not enough to do a thing for a dog as large as Fran's!
Bubba's 65 pounds, and he gets 4-5 benadryl per dose. He used to get at least twice a day, but when he got that stomach crud, we stopped and have just been living with the snot. The dosage is 1/2 mg to 2 mg per pound, and the caplets are 25 mg each. I think Elizabeth is a Great Pyranese, and probably at least 85 lbs, so a dose for her would be anywhere from 45 mg on the low end (two tablets) to 170 mg (seven tablets).
Fran is probably right to call the vet, though. Just don't spend $4,000 on it unless she seems sick in other ways too!