My wife concurs that Hidelisa is a good possibility. They are located on corner of Antera Mota and San Felipe.
For a broader selection of material, check out La Epoca in Santiago. 30 de Marzo, #16. Beautiful material. There is another place nearby owned by a relative of the owner of La Epoca that you can also check.
If it was Barbara looking for material, she would not buy until she checked La Epoca. They have a lot of imported material from Europe, much of which is wider (108") than national material.
There are some excellent seamstresses in the Sosua area.