Just to confirm the rule here... The object takes the genitive in a negative sentence? Otherwise (without the nie) it would be "widzę dziewczynę"? Also I thought the genitive ending was dziewczyny? These cases will the be the death of me. Had no issues with Latin / German, but this is nuts! Thanks for any enlightenment!
What exactly did you write?
'Dziewczynki' can be either singular genitive or plural nominative/accusative.