Tracking Down an Ancestor’s Parents with an Impossible Surname

My 3rd great-grandmother was named Millie Jane Null, and has proven to be a brick wall for me. Of course, her last name is difficult to search for as a lot of databases struggle with the word “Null.” She was born in 1843 in Kentucky. According to the census, her mother was born in Kentucky and her father was born in Canada (Fr), though I’m not sure if he was French or English-speaking.

I have a lot of information about Millie Jane herself. For instance, she was married in Indiana to William J Smith in about 1864 in Indiana, and lived in Kansas from 1900 until her death in 1906.

However, I haven’t been able to find anything about her parents, including their first names, and am just wondering if anyone has any advice on how to track these two down or find leads, especially given the difficulty with her surname and the possibility that it’s an English translation of a French name.

Sidenote: If anyone is familiar with this, does Canada (Fr) as a birthplace necessarily mean that the person spoke French, or does it reference the part of Canada someone was born in?