Its very important for the girl to take it in (5)
I believe the answer is:
vital
'its very important for' is the definition.
I can't judge whether this definition defines the answer.
'girl to take it in' is the wordplay.
'girl' becomes 'Vi' (short for Violet).
'to take' becomes 'al' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'in' means one lot of letters goes inside another.
'vi'+'al'='vial'
'vial' enclosing 't' is 'VITAL'.
'the' is the link.
Can you help me to learn more?
(Other definitions for vital that I've seen before include "Spirited" , "Most important, like certain body organs" , "Are such statistics" , "Crucial" , "Essential; lively" .)