Her hero William is in the Salvation Army (6)
I believe the answer is:
stella
'her' is the definition.
'william is in the salvation army' is the wordplay.
'william' becomes 'tell' (I've seen this before).
'is in the' indicates putting letters inside.
'salvation army' becomes 'SA' (abbreviation).
'tell' going inside 'sa' is 'STELLA'.
'hero' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for stella that I've seen before include "girl!" , "lady?" , "____ McCartney, fashion designer" , "woman" , "- Gibbons (Cold Comfort Farm)" .)