A couple of thoughts come to mind:
1. She's doing it for attention- maybe the negative behavior is the only way she's getting the attention she needs, even with less than desirable consequences.
2. Have you considered that perhaps she has OCD? The frequency with which she's doing it is what makes me think it might be an underlying factor. I used to have an OCD issue with my hair growing-up and even into adulthood, though I didn't chew it.
2. I am having a hard time understanding why these are behaviors punishable by time-outs. Boogers don't gross me out though it's not an acceptable behavior, but is it a punishable behavior in that manner? Seems a little extreme for me. Have you tried making sure she always has access to tissues and praising her when she uses a tissue vs. her fingers?
It does appear that a condition called impetigo may be caused by staph bacteria from the nose coming in contact with broke skin:
http://en.wikipedia.org/wiki/Impetigo