I'm so sorry. There is nothing like the feeling after hearing that news. Depending on the type of OS, and whether it has spread there are options. As Winnie's mom said there are stories here Hope for Hounds to give you hope.
Take things one step at a time, contact Dr Couto, gather your information, make an informed decision. That's all Snickers can ask of you, well that and your love but she already has that.