Because she doesn't fit your stereotype of what a maker looks like, and that challenge to your preconceptions can either be accepted or rejected. Some percentage of people will reject the challenge, and come to the conclusion that this person is not who they claim to be.
In short: sexism.
For further reading, see criticism of the "fake geek girl" meme.
In short: sexism.
For further reading, see criticism of the "fake geek girl" meme.