Translation:Which country is Maria from?
I interpreted it as a question, "Maria, what country do you come from?" Which should also be correct depending on the context.
Strictly speaking, it should be: "Which country was Maria born in?"
Almost everyone I've met asks 「どの国から来ましたか？」. And when I reply with one of イギリス, 英国, or 北アイランド, they would then typically go:「ご出身は？」。
In this context, the correct translation is: "Yes, but where are you really from?"
Exactly. Usually I hear, 「どの国から来ましたか？」Then if hometown (出身) is mentioned, they want to know which city in your country. This one confused me a bit because I thought it was asking about Maria's hometown. I got native confirmation that some people use this phrase to ask which country someone is from.