Another biting question

[reddsurion]

1 1/2 year old red tail approx. 4 1/2 feet long. gotten when she was 6 months old. Saved her from a bad environment. handled daily and fed regularly since we got her. Usually she's fine and can be handled with out a problem but today she bit and held on for dear life. Took two people to get her to release. The bite is a deep one. I also started to wonder if she didn't have snapping turtle in her also....lol.
she has biten before this also without warning or cuase that I can see. She's fine calm and relaxed and then one day she bites.
Have put the cloth in the tank, Have increased handling amount and shorter times. even gone as far as letting her lay on me sleeping.
As I siad before she seems fine and relaxed and now problems then she just all of a sudden bites for no apparent reason and now she has gotten were she hangs on.
I have read every post I can on biting even the ones on retics
Any ideas or thoughts?
Thanks in advance,