Hi J. - I fully understand how you feel about the situation. OK. I have an 12 year old nail biter - feet included! - how gross it that? I have a 9 year old destroying machine when it comes to clothes - chews off buttons, collars, t-shirt neck bands. They are not going to stop until we can figure out WHY they are doing it. For some it really is just a phase though.
Last night I caught my 10 year old putting her hair in her mouth - this is a new thing. I can remember doing it too when I was probably between 7-10 (somewhere in there) I am 47 now so it is hard to be precise!!
My son has bad ADHD, plus he has nervous energy and he stutters, so he has an oral fixation. The speech teacher at school gave him a rubber "P" that is made especially for special ed students. He stopped chewing up pencils once he got that. I have to sanitize it daily but he likes it. I will not allow gum for my kids but that could be an option for some.
Trust me I have tried talking to them, shaming them, the eating germs thing, paint on polish (nails), putting tape on the fingers at night, taping gloves on to hands at night,
spraying "bitter" spray on to clothes accessible to the mouth, a giant reward program, extra allowancs, treats and so far still no nails growing, still chewed on clothing in the laundry. Habits have to be changed. I fear that if you cut her hair she might replace that with something else - then what?
Some times we, as parents, have to learn to ignore it - providing they are not hurting themselves or anybody else.
Have you tried putting food coloring on the end of say braids? if she is blond - use yellow, dark haired use red and when she puts it in her mouth it will turn her mouth that color - at least you will know if she has done it or not.
Good luck with what ever you decide.
M. F