Can Cancer Come Back At Stage 4 Even After Receiving Chemotherapy?

hello there ... I have a question, and im very confused about the info im getting from my friend who has brain cancer. She first was diagnosed about 6 months ago .. tumor was located right behind her right ear. She went through chemo/radiation and finally doctors were able to go in and surgically remove it. After that she said she was to have chemo once a week to eliminate anything else that possibly might be there. Then today she just was told the cancer came back.. same location and spread to her neck... she said the docs told her shes stage 4 ....... can it come back that fast at a stage 4 ?? ... even if she was receiving chemo once a week???? Shes got me depressed because shes talking about just quitting treatment and giving up... I don t know what to do to help her