You can actually speak with any Arab, guy or gal, without declining nouns for case at all. Noraurora is correct about both being correct. Arabic is what Arabs speak; Arabs can never be "wrong" when speaking their language. Anything they say automatically becomes correct Arabic.
Dawn6914, I think, in formal MSA, it would be nominative declension. Read this blog:
If the sentence was something like "I see your grandmother", it would be jaddatAka (accusative).