Fairly doubled up? That's too cute (6-6)
I believe the answer is:
pretty-pretty
'too cute' is the definition.
(I've seen this before)
'fairly doubled up?' is the wordplay.
'fairly' becomes 'pretty' (I've seen this in another clue).
'doubled up?' says to double the letters.
'pretty' doubled is 'PRETTY-PRETTY'.
'that's' is the link.
(Other definitions for pretty-pretty that I've seen before include "Twee" , "too cute" , "Knick-knack; over-dainty" .)