Breast Cancer Triple Negative _ Relapsed

My mother was diagnosed with breast cancer (TNBC) in November 2017. She underwent surgery (After surgery doctor said he couldn't remove 1.8*3.8 cm of tumour since it was attached to right axilla. Removed tumour was 17cm in diameter) followed by chemotherapy ( 4 chemo +12 paclitaxel + 3 chemo (gem +carbo) till 8th September 2018. Tumour didn't respond to any of the these. Now it has grown about 12*18cm . It has also spreaded to liver and abdomen. Now doctor is saying he wants to test the removed tumour again because he got doubt that primary place of tumour was not breast. After testing it, he will see if there is some other treatment accordingly . Till then he has prescribed ENDOXAN tablet. (Surgery was done in different hospital and chemo was given in different hospital) So, my question is...things like this happen? Will there be any solution? Attached is the first CT &latest PET report My mother has become very weak because of these chemo. Not sure if she can sustain further chemo.