Her Victor's back in Siam! (5)
I believe the answer is:
mavis
'her' is the definition.
'victor's back in siam' is the wordplay.
I cannot quite understand how this works, but
'victor' could be 'v' (phonetic alphabet: alpha, bravo, charlie etc.) and 'v' is found in the answer.
an anagram of 'siam' is 'mais' which is located in the left over letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mavis that I've seen before include "Girl's name - song thrush" , "bird" , "Fem. name, song thrush" , "Girl" .)