It’s a well crafted theory, but unfortunately ultimately incorrect. She is clearly a Skywalker. Does no one recall one of the earlier trailers where Luke says,
“ The Force is strong in my family. My father has it. I have it. My sister has it. You have that power, too.”
Who else could he possibly be talking about? And before anyone says Kylo Ren, why would he refer to Leia as “my sister” and not “your mother”?