"My dog died last week."
I see that the contributors are now accepting the two interchangeably. I would still caution users to remember that 死にます means "to die", while 亡くなります is a euphemism closer to "pass away". I would also caution users that they might unintentionally come off as strange to some native speakers when using 亡くなります to talk about pets.
This HiNative answer says:
Q. Is 亡くなる then reserved for humans only?
A: No. It depends. If the owner of the animal is someone you respect and admire, you could use 亡くなる
△僕の犬が今日亡くなってしまった。if you want to show your respect to your dog, or you really treat him as your human family, you could use 亡くなってしまった
In general in Japan:
⭕️ = correct
△ = not perfect but okay
X = incorrect
Both「犬は先週死にました」and 「私の犬は先週死にました」were marked wrong. I believe this should be correct? I reported it.
I can't understand it because in another lesson of the same section,「彼女は去年離婚しました」has a similar structure but is correct...
Or is it incorrect to use は as a topic marker when talking about someone passing away?..
In the same way that you drop subject pronouns, you can drop possessive pronouns in Japanese. If I say 手が痛いです (te ga itai desu), I usually mean that "my hand hurts", not just any hand. The same with 犬が死にました (inu ga shinimashita), it can mean "a dog died", but it's also perfectly reasonable and correct to interpret it as "my dog died".