M.F.
Hello M.. Well, my 5 year old had that same issue. She was terrified of the larger carseats; especially if there was a part that came over and touched her knees. You may have to take it back and find a seat similar to the one that you have for her now. Or try a pink one...try taking her with you and letting her see what is out there and let her pick it out. Make it a day out, just the two of, and ask for help getting the carseats down from the shelf so she can try the ones out that she likes. Trust me, that is way better than listening to a screaming, terrified toddler. :)
Good Luck to you!
M.