Due to the laws at the time, she had to be 19. She was right at three months shy of confering US citizenship to him. He was born in August while her upcoming 19th birthday was in November.
I don't see a minimum age in Clause 5 for the future president's parents to confer citizenship onto the newborn. Was there one stated by the founders in other ways (i.e. federalist papers)? Or was there one in English common law at the time? If Yes to either one, then what was the minimum age? Or if No, then I have to conclude that the founders didn't intend for a minimum age for the parents to confer naturalized citizenship.
Either way, I don't see how a law passed by Congress can change the Constitution's requirements for President. Only an amendment process can do that. Think about how dangerous that is to let the 1952 act change the presidential requirements. Will we, therefore, let a future law completely change the presidential requirements (again without going through the amendment process)? Look at how much I want to honor the 14th amendment's "subject to the jurisdiction thereof" requirement for citizenship as it was originally meant, not how some law or judge tried to redefine it without the amendment process. By getting away from how it was originally intended, we have anchor babies galore.