It will be in FLorida and we will be on I-95 a few times. The CCO is borderline outgrown. I can't really tell if she is within an inch - she's probably about 3/4 or 1/2 inch from top - too dangerous? Worse than FF?
To tell if a seat is outgrown, buckle her in as usual and get a book that is 1" thick and rest it on her head (she's going to give you a weird look, fair warning), angle it so that it is perpendicular with the back of the car seat (not parallel to the ground) and see if it is below, even with or above the shell.
If she's less than one inch from the top of the shell then the seat absolutely cannot be used RF. An outgrown RF seat is not safe, a properly fitting FF seat is safe. When it comes to the one inch rule, it's very set-in-stone. When she rides up the back of the shell in a collision the seat is designed to protect her head and body and keep it within the confines of the shell. They have tested it with this rule and it has passed with this rule. Yes, there are other seats (the Cosco Apt is one such example) that have a "head even with the top of the shell" rule, but that is a different shell with different harness geometry, has different belt paths, etc. So who knows. The CCO may have been tested that way and failed, or has not been tested that way at all, and IMO its not a risk you should take
It's a good question though, very valid thinking but it's a rule that absolutely should not be broken. It's not like taking an infant insert out at 21lbs when the manual states "use the infant insert until 22lbs".