We just got baby chickens that are 1 or 2 weeks old, when one of them is falling asleep she keeps twitching/flicking her head. Is this just because of the wood shavings or does she have a nervous twitch, and how to solve it?

Wood shavings. Most baby chickens sleep under a mother's wing. Since mother's wing is absent, slightest unfamiliar around will cause light sleeping and twitching because it feels unsafe since it isn't covered. As it will get older...it'll be fine. Maybe a tent like structure over the nest to give it a more protected space may help. Chickens like nests in enclosed areas. My neighbor used five gallon empty paint buckets screwed to a board (on it's side) as a nesting holes in the chicken coup.

I bought six baby chicks and put them on wood shavings, just like they did where I bought them.  The chicks did OK at first and then after I changed the wood chips which came from deeper into the wood shavings bag, my chicks began twitching their heads.  One of my chicks died.  I noticed that if I moved the heat lamp away from them they did a little better.  Anyway, I decided to change the wood chips again later and they twiched their heads even more.  I got a bowl of the wood shavings and put them close to my nose, and the wood shavings were too strong for me to smell.  The poor chicks were inhaling a very strong odor.  I totally removed all of the wood shavings, and covered their area with white paper towels and all the twitching stopped within fifteen minutes.  After that they did just fine.  Don't use the wood shavings with baby chicks, because sometimes the wood shavings have too strong of an odor for the baby chicks tiny lungs.

I am not saying your chick has this:  ... But one of my baby ducklings had this symptom, last year. It then became more frequent and she started to develop a sort of sneeze with the twitch and head flick.  Sadly its breathing got worse and we had to have her put to sleep. It was very upsetting.
I suggest you make sure the chick is OK by visiting a vet.