Goes too far with mistress, having failed at first with other females (8)

'goes too far' is the definition.
(to overdo is to go too far or do excessively)

'mistress having failed at first with other females' is the wordplay.
'mistress' becomes 'lover' (I've seen this in other clues).
'having failed at first' means to remove the first letter (the first letter fails to appear).
'with' says to put letters next to each other.
'other females' becomes 'does' (female deer. I am not sure about the 'other' bit.).
'lover' with its initial letter taken away is 'over'.
'over'+'does'='OVERDOES'

'with' acts as a link.