First thing you need to know is this:
I have been told that this type of cancer cannot be cured...but we can do things to prolong life and make it better....
Having said that, some people do get cured...and usually these people are younger, healthier people....being 30 years-old, your sister is young and surely her body is stronger than someone much older...
So the reason they can't tell you what's next, is because they wanna see how good the chemo will be...hopefully the chemo kills the cancer and reduces it to the point where it's unnoticeable...after that, they might decide to do surgery, followed by more chemo...
It's a never ending battle...she will have to fight it...but she can win this battle...don't always listen to doctors... most of what is said is averages and estimates..my mom was giving a 5% chance to live past 6 months and she is still with us...