I'm not sure what style it is but you can buy the bag here .. well its in purple and silver stud things .. theres others on the website too - balenciaga
I'm not sure it's the same bag...Stam's looks rounder and saggier and the strap looks longer, I think. I'm suspecting it may be this one, in fact, except hers is in black. But thanks for the link, it's definitely similar to the Arena...