My daughters hair is super thin

(She just got out of the bath)

We do trims all the time, when she was a year I did what everyone said to do and gave her a bob. I don’t want to chop it all off again, it’s growing out but it’s staying thin. I recently just changed to actually ponytails instead of the hair elastics because they would rip a lot of her hair out.

Any suggestions on what to try??