"If you wanna get super technical," she starts, making another face, sure that this answer is just as boring as the last, "I learned to sew in high school. We had to do this one project, where we had to make, like, this ugly 1800s Amish, No Ankles Visible Because Ankles are Improper kinda dress, and I decided that sucked, so ... "

So, she made something more modern on her own, with fabric left over from the project as she did it. It hadn't been terribly good, but -- well, she'd gotten better from there with time and practice, until, yes, she was making her own costumes.