If she is still in her infant seat, consider purchasing a convertible for her. The more upright seat will likely pacify her, my boys never liked layng back in the car seat, but were perfectly content to sit in the convertible (and both rear faced the car for 18mos (oldest) and 35mos (youngest))
Evenflo Triumph ADVANCE is a great seat for around $130. It will rear face to 35lbs, forward face to 50lbs.
Graco MyRide 65- also a great seat! Rear facing to 40lbs, forward facing to 65lbs. $150, but you can find it at Bed Bath and Beyond right now for $99! GREAT deal.
If you need a car seat, Babies R Us is also hosting their 'Great Trade in Event' where you bring in a piece of old baby gear (like your old infant seat) and get a coupon for 25% off a new one. You can get the My Ride for $97 that way.
Also make sure she's not too hot. No BUNDLE ME covers, no BUNTING SACKS, no WINTER JACKETS! These things are all DANGEROUS in the car seat. All she needs is a polar fleece coverall or a polar fleece jacket and a blanket to stay warm in the car, with a hat and mittens. Nothing thick, bulky, or that reroutes the harness like the Bundle Me in the car seat. EVER. If you are using these things, remove them immediately.