Such sketching is in sha Allah permissible as long as you don’t show
the features of the face. If you avoid putting a head altogether, that
would be even better.

If the audience are all women, this is permissible. But if there is a
single man, this is totally prohibited even with hijab.

Iam a fashion designer so is it allowed for to sketch my clothes designs with out any facial features but with hair and if Iam making a dress intending that it’s for a female gathering and I wanna showcase it to my audience with a non Muslim model should I follow the rules of hijab on her as well