"This woman's cat is white."
Translation:Die Katze dieser Frau ist weiß.
I put "Der Katze von dieser Frau ist weiß." and was marked wrong, and it said the correct answer was "Der Kater von dieser Frau ist weiß." -- and when I was asked the same question a second time I used "Der Kater von dieser Frau ist weiß" and it was marked correct. I'm not sure but think this means the woman's hangover is white? -- if this describes the state of the Duolingo expert while putting this answer together, we should, of course, be kind, and wait until she has had ihr Kaffee (2017 Aug 7)
Katze is grammatically feminine, so you should have used die Katze if you wanted to use that word.
der Kater is, as Mr_Eyl wrote, specifically a male cat.
Unfortunately, Duo isn't smart about correcting adjective endings or wrong-gender articles (i.e. assuming that the noun is correct) and instead assumes that the first word is correct if possible.
'Kater' is a euphemism for a hangover. Its literal meaning is 'tomcat'. A 'Katze' is, strictly speaking, a female cat.