2yr old making lip bleed

My 2 and a half yr old started biting or picking at her bottom lip till it bleeds about a month ago.  I tried ignoring it cause she did it when she was bored (like sitting in car seat on the way to store) and figured if I said anything she would do it more.  But now she does it all the time and it really bothers me.  I've found blood on her sheets and sometimes she looks like we've socked her in the mouth there is so much blood!  She hardly ever does it when she is angry... mostly when bored or tearful.  The tantrum stage is kicking in as well and not wanting to sleep in her room at night.  I've tried putting lip balm on her lips but not helping.  Is this a way for her to vent frustration?  Something I should take her to the doctor for?  She's a loving, playful gal who likes to get into everything.  Her speech is so-so.  She says some things that are around 4 or 5 words long, but uses still a lot of one word wonders to get things she wants.  (Milk when she wants milk.. not I want milk, etc)  She knows most of her alphabet on site, counts to 13, points/knows body parts, knows some shapes/colors.  She has a 6 yr old sister and i'm a stay at home mom (married, hubby is active with girls).  Any ideas?

[DustyL]

Give her something to do in the car to occupy her (a book perhaps) Explain to her that for every time she is caught biting her lip in boredem she will be sent to timeout for 2 minutes. If there are times where she speaks her issues instead of biting her lip reward her (positive attention and praise are some of the best rewards) Also, when you notice something is bothering her or a common time where she would bite her lip... stop whats going on and talk to her. Give her the words she needs to explain her issues and as important make sure she understands what they mean. Try reading Lynn Clark's book SOS Help for Parents there are a lot of good suggestions to help you stop bad behavior and start good behavior. Good Luck