"Mijn zus wil een katje."
Translation:My sister wants a kitten.
No, the third person singular (he, she and it) is always 'wil'. This does not happen in regular verbs, where the second and third person singular always end on a -t.
As an addition, using 'wilt' with 'jij' also depends on the dialect, I suppose. I almost never say 'jij wilt'. But maybe other natives do.. ;)