I kept all my kids in shorter rackets longer than most and it probably hurt their early tourney results but I feel it contributed to some very good technique.
In particular, having a shorter racket that you can 'wield' better will greatly help with volleys, especially one-handed BH volleys, slice BHs, overheads, and nice serving motions. Also, having a racket proportional to the kids height will help with 'scramble' type games/drills where you get put into more defensive/improv situations including slice backhands, squash forehands, reflexive situations. Heck, even tweeners
I personally think especially girls lack the ability to improv. I.e. most have no idea how to run down and flick a lob over shoulder or play the ball in other awkward positions - and putting them in a big racket too early certainly won't encourage it.
The full size racket for that young of age might help give depth and pop in tourney play on the FH and 2 handed BH, but I feel it inhibits you on technique with regards to serve, volleys, slice BH. It's about levers and proportions. A five foot kid leveraging a 27 inch racket would be like me trying to play with a 32+ inch racket...which would be very challenging and frustrating.
This all said, choices can be limiting but there are a number of quality 26 inchers out there. (Also, the Babby TCF mentioned is a great first 27 inch racket...I woudl just hold off until she's 5 feet at least).