She may have partnered Den as a girl (3)

'she may have partnered den' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'a girl' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
The remaining letters 'mi' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

'as' is the link.

Can you help me to learn more?