jeff-hauge definitely gave the best answer, but there are smaller things as well. Her father mentioned things being "all slung about" but Mayella never mentions things in the room being bothered, just that she had "fought 'n hollered" and he threw her to the floor. Also, her father said that after Tom ran off, Mayella was "lyin' on the floor squallin'" but Mayella says she "sorta fainted an' the next thing [she] knew Mr. Tate was pullin' [her] up up offa the floor."
And of course, there's always Tom's testimony where he says "She says she never kissed a grown man before an' she might as well kiss a nigger. She says what her papa do to her don't count," which is probably the most damning thing for the Ewells' testimony... but of course coming from a black man, it's largely ignored.
Aside from Mayella's bruises there is one very important contradiction between their accounts.
Bob Ewell saw clearly who attacked his daughter, but he was caught in the fence outside his house. But Mayella says her father barged in and yelled, "Who done this to you?"
Will each had one thing in their testimonie that fit but it didn't connect to the story like if your putting a puzzle togather and you think one piece goes in one spot put seems to not fit but it looks like it goes. They each had one thing in its wrong place.