The Marcher Look ‘n’ Feel for magic users is remarkably sparse, from memory it is something like “mummers wear bright colours, landskeepers sometimes dress in robes like friars”. Also almost all of the traditional fantasy elements that would be associated with a witch or wizard are specifically mentioned on some other nation’s Look ‘n’ Feel. Pointy hats and talismans are Varushkan, runes and danglies are Wintermark, ornate staves are Dawnish, simple staves are Urizeni, tattoos are Navarri.
If you try to create any of the look of a traditional fantasy witch you will therefore end up treading on aspects of other briefs. So do so, lots! Tread on several, keep it simple and avoid the more distinctive other aspects. Pointy hats may speak Varushka, so make sure to avoid the patterned edging and use the Marcher palette. My character carries a mask, which may seem League, but it is made from straw and beads. My character wears runes, which may seem Wintermark, but they are pyrographed and floral. Also Poppets. Poppets are really easy to make and very distinctively Marcher.
Finally you’ve specifically mentioned Hedge Witch, this is great, and that is a magic user attached to a house. You may wish to think about how this attachment is telegraphed through the costume. Do they carry a simple belt sash, do they wear the house tabard?