"The girl has a dolphin."
Translation:La ragazza ha un delfino.
Sad question and the sad truth is that some people have smuggled wild animals of all kinds to animal "lovers" (not) who want to be "special". These wild animals suffer and die whilst being transported, they mostly lead bad lives in cages, lots never see a vet because they are kept secret.
I would like to see other sentences at duolingo. Sentences about animals roaming free in the wild. About people taking care of them. Kids looking at a butterfly in the garden or birds in the sky. Animals living in a "forever" home.
The sentence is "The girl has....", so the verb "ha" goes with the girl, which is the subject of the sentence, not with "the dolphin" which is the object in the sentence. Also, "ho" is "I have" while "ha" is "he, she, it has", which is what is needed for "the girl". I hope my explanation is clear and helps.