"This girl is my daughter."
Translation:Tato dívka je moje dcera.
Here are more possible options - Ta is acceptable as well (or should be acceptable)
No Damek96, "ta" is "that" or "the", but not "this". This DL course is quite consistent on that point.
Shouldn't it be "moje dcery" i.e. genitive form of dcera? If not why not?
To be be something always uses nominative. Or sometimes can be instrumental.
Why do you think it should be genitive? Is it because the word my/moje suggests genitive to you? Well, that is not the case (so to speak!) Possessive pronouns do NOT govern the genitive.