What Causes Red Blister Around The Anus?

hI, MY 3 YR. OLD DAUGHTER HAS LITTLE RED BUMPS WITH WHITE CENTER AROUND HER ANUS. SHE DOESNT COMPLAIN ABOUT THEM EXCEPT IN THE TUB OR USES THE BATHRROM...ONLY WHEN SHE IS BEING CLEANED SHE CRIES THAT THEY HURT. WHAT IS THIS? I SEE THEM NOWHERE ELSE ON HER BODY AND I M SUPER CAREFUL NOT TO LET HER SIT ON BARE PUBLIC TOILET SEATS