Time to run through the list (some are pretty "duh", please don't take offense):
Medical Schtuff
- Motion sickness (esp common in kids with ear problems)
- Does she get yeast infections/diaper rash (in which case the forced position can create a lot of pain)
- Allergy to the seat materials
- Too loud (ear protection works with a lot of children with sensory issues)
- Too bright (sunglasses... ditto sensory issue)
- Sensory overload
- Ear pain (having a bottle in the car usually fixes the not being able to "pop" your ears thing that babies have)
Pain/ Adding insult to injury
- Is the seat comfortable / have you tried different seats? (My son actually had a lump in the back of his seat from a strap under the cushion that would dig in him... it took me a solid MONTH to figure out why he all of a sudden HATED his car seat -new problem-, other seats just are shaped as wrong as possible for certain babies)
- Wrong angle for the seat? (too upright is usually the cause)
- Straps long enough not to be biting/rubbing
Mental/Emotional
- Scared (will she sit happily as long as she can SEE you; like in your home?) if so... you may try forward facing the seat if a mirror isn't good enough. (I know)
Ugh... there's more... but my brain has shut off.