Stanley Ann Dunham was born on November 29, 1942, in Fort Leavenworth, Kansas. So, she was a US citizen. I know of no evidence that she renounced citizenship, and there is evidence (passport) that she retained it.
Barack Obama was born born August 4, 1961, which was before Stanley Ann Dunham's 19th birthday.
Now, I'm not saying this changes your answer to my hypothetical from "yes," but one of the conditions you stated appears to be unsatisfied.