Her choice is between a dizzy head and a heavy heart (4)
I believe the answer is:
dora
'her' is the definition.
'choice is between a dizzy head and a heavy heart' is the wordplay.
'choice' becomes 'or' (I am not sure about this - if you are sure you should believe this answer much more).
'is between' means one lot of letters goes inside another.
'head' says to take the initial letters.
'and' means one lot of letters go next to another.
'heart' indicates the central letters.
The centre of 'heavy' is 'a'.
The initial letter of 'dizzy' is 'd'.
'd'+'a'='da'
'or' put inside 'da' is 'DORA'.
Can you help me to learn more?
(Other definitions for dora that I've seen before include "David Copperfield's 'child-wife'" , "Bryan" , "This girl" .)