Looks like it's just Sindel's normal alt. I don't use her a lot so I don't recall what it was, but it's certainly Sindel, no question. Also, if it was klassic for her, she wouldn't have a ponytail from what I remember.
I thought so too but Sindel doesnt have a pony tail in any of her costumes in MK 9. It does look like Sindel but I have never seen her with a pony tail and her main alt has trench coat tails on it and her second alt is more of a regal look to it.