Suggest Treatment For A Lump Inside The Vagina

MY FIANCEE HAS A HARD LUMP INSIDE HER VAGINA, IT ONLY APPEARS IN OR AFTER A HOT BATH. WE JUST TRIED TO HAVE SEX AND IT FELT LIKE A HARD WALL AGAINST MY PENIS. WHEN WE CHANGED POSITIONS TO MISSIONARY IT SLIGHTLY WENT AWAY UNTIL IT DISSAPPEARED. SHE HAS RECENTLY HAD A CHECK AND THEY SAID NOTHING IS WRONG. ALSO SHE HAS HAD A SMEAR AND IT CAME BACK FINE. WE HAVE 2 CHILDREN. SHE IS WORRIED IT IS HER WOMB, BLADDER OR CERVIX FALLING FORWARD. DO YOU KNOW WHAT IT COULD BE?