This may sound a bit far-fetched, but hear me out. When Willow was a girl, she somehow made a Terrorbeak, a very powerful shadow creature, retreat with just a teddy bear. Then, with no way to make fire and with the "flammable materials" in the closet, she somehow set a conflegration that burned down the entire orphanage. We did not actually SEE how the closet caught alight, so it is perfectly possible that Willow set it on fire with pyrokinesis, similar to Charlie in Stephen King's Firestarter (but it's not the night-monster Charlie, don't worry). In Firestarter, Charlie manifests her pyrokinesis by setting her teddy bear on fire when she was at least a year old. Willow was highly based off of Charlie. So, is it possible that, like Charlie, Willow could have pyrokinesis as well...? Let me know!