Because the family had contacts in nearby Seattle? Plus Stanley Ann herself had many friends living in the area, since she had graduated from Mercer Island High School.
If she was supposed to give the baby up for adoption, Canada would at that time have been a much better spot for a mixed race baby to be adopted by a "good" family, than the US would have been.
All the "paper work" of getting admitted to U Washington would have already been completed before August '61, so why not stay there with the baby. Might have also been part of a "sham marriage" deal with BHO Sr. It's pretty apparent that she never lived with him after BHO Jr. was born, and perhaps not before either.
All certainly possible.
The Contacts and friends in Seattle sort of cut against your thought because if she was getting out of the way because she was in an unfortunate pregnancy, she wouldn't want to be accessible to contacts and friends. Further, if that had happened, they would all have known exactly what happened and yet none of them said anything about it when they were being interviewed when he was running for President.
Don't think a mixed race baby would have had any reception in Canada in 1961.
I don't see what the last paragraph adds to the analysis. She might have enrolled by mail at the U but in the fall of 1961, the U of W was a relatively looser operation.
She didn't stay in Seattle because whoever was paying the bills and calling the shots wanted a record that he was a citizen in Hawaii and thought it was important to get him there.
If I had been in charge of her record, or her mother's effort, I would have got the kid back to Hawaii as soon as possible after birth; called one of my doctor friends who delivered babies at one of the local hospitals; got birth document forms filled out complete with the footprint; and had him slip them into the stack with the rest of his deliveries at the hospital. If she'd done that, we wouldn't be having the discussion even though we know he was born in Mombassa.
Questionable what they did do but I think they took him back to Hawaii because the planned to do something to report his birth that required his presence. Further, I suspect that given the fact that she had been living the last six months with his family in Kenya, they all hoped that she would just move back in with him and establish a happy little family while he was in college at U of H.
The decision to send her to the U of W was made in later August after it appeared that dreamworld wasn't going to happen.