I fought it for long enough that I can confidently say it's part Electric. [Hence the static frizz of her hair.] There's definitely some dual-typing going on, but I haven't nailed down what the second one is yet.

[She frowns at the Rotom, who narrows its eyes right back at her.]

When it wasn't zapping us it was hurling leaves everywhere, but none of its other attacks reminded me of a Grass type. And look closely... You can see it, right? There's a strange green aura surrounding its body.