Yes. A stickler might argue that you should say "a/the portrait of my mother" (I'm assuming that's what you mean), in order to avoid any quibble that "my mother's portrait" should mean "a portrait belong to my mother" rather than "a portrait depicting my mother". However, in your sentence the latter meaning would normally be assumed anyway.
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Gene93I realize it might be a little ambiguous, but is it unnatural?No. Hence my original answer "Yes" to your question "Is it natural?"