In the Wikipedia page about the 2017 French presidential election, we can see the demographics of the vote, whose source is Ipsos
https://en.wikipedia.org/wiki/2017_French_presidential_election According to the data 89% of the self declared centrists who voted for one of the candidates in the runoff voted for Emmanuel Macron, and 11% voted for Marine Le Pen.
Who is this centrist who voted for Le Pen?
Some hypothesis
1) A far-right person who answered in the poll that considered himself/herself centrist in order only to show that not only far-right people voted for Le Pen
2) A centrist feminist who considers that the victory of Marine Le Pen would be important for women empowerment
3) Someone who doesn't know what does the left/center/right politics mean and answered "center" because didn't know how to answer the poll
I believe that the hypothesis 3 has the lowest probability because since France is the country where the left/center/right politics was born, I believe it's hard for a french citizen not knowing what does it mean.