。
She has a scarf wrapped around her neck.
Literal
She [topic-は] neck [around-に] scarf [object-を] is-wrapping.
スカーフをまく (to wrap a scarf) uses まく (巻く, to wind/wrap). 首に marks the location — around her neck. The ~ている describes a resulting state: the scarf is currently wrapped and staying there. This [body part] + に + [item] + をしている/まいている pattern is standard for describing what someone is wearing on a specific body part.