Not in position to admit girl that's too good to ignore (10)
I believe the answer is:
unmissable
'too good to ignore' is the definition.
I can't tell whether this definition defines the answer.
'not in position to admit girl' is the wordplay.
'not in position' becomes 'unable' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to admit' means one lot of letters goes inside another.
'girl' becomes 'miss' (term of address for an unmarried woman).
'unable' placed around 'miss' is 'UNMISSABLE'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for unmissable that I've seen before include "that cannot be overlooked" , "Not to be forgone" .)