She's in double figures (4)
I believe the answer is:
mimi
'she's' is the definition.
'double figures' is the wordplay.
'double' shows that letters should be duplicated.
'figures' becomes 'mi' (I can't justify this - if you can you should give a lot more credence to this answer).
'mi' duplicated is 'MIMI'.
'in' is the link.
Can you help me to learn more?
(Other definitions for mimi that I've seen before include "I'm upset twice by the operatic girl" , "'They call me - - ' , (Lucia)" , "I'm, I'm mad about the heroine in 'La Boheme'" , "showgirl" , "Bohemian girl" .)