I Have A Niece That's 9 Months Old----at About 4

i have a niece that's 9 months old----at about 4 months she got a rash in the bend of her arm.....doc said it was yeast infection due to slobbers.....then the rash looked exactly like ring worm, so the doc stated it was ring worm....it them went with vengeance to legs arms belly back of neck....he now says its dermatitis ....how do we know for sure without going to dermatologists (which is over 100 miles away)this rash does itch her...do you have specs on pics of allergy rashes..etc ..?? THANK YOU FOR ANY INFO>>RESPECTFULLY....Lori & Maddie