Make sure you have a convertible car seat, install it rear facing and use it for her. She doesn't need to remain in an infant seat for a year, my boys were both in a rear facing convertible car seat by 5mos old.
A rear facing car seat is outgrown when there is less than one inch of hard shell above the childs head or the child goes over the weight limit for rear facing. When one of these things happens, move to a rear facing convertible car seat. The AAP, Safe kids, and NHTSA recommend children remain rear facing until the yare at least 2yrs and 30lbs, and its best to keep a child rear facing until they outgrow their convertible car seat rear facing. The harness should come from just at or BELOW the shoulders for rear facing.
Please visit safekids.org for installation help, and carseat.org for more information. A child should never be forward facing before 1yr, and really no child should be forward facing before age 2. If your car seat is forward facing only, buy a convertible car seat that can rear face, then forward face. Please message me if you would like suggestions on seats that will last hte longest and keep your child safe.