This is a patient forum and for support... so I can’t give medical advice as you are requesting.
I have had two family members with aggressive brain tumors, an uncle and my father. Some people like my cousin was able to control his for a while, but my other two family members were not able to do much a passed rather quickly (6-9 months).
There are so many factors at play like genetics, lifestyle before the tumor (smoking or not, healthy or not etc) and doctors are going to try try try, but at some point, treatments are going to cause more pain than the tumor... so while it is hard to face, she has to discuss with the family, if she can face it, her final wishes and have things in order and decide when she wants to stop treatments and do palliative and then hospice care.
The doctors can also consult with other hospitals for other protocols but it sounds like they are covering all bases.
I am so sorry to hear about your sister...
Thank you for your answer and advice