Regular screening required after masrectomy?

My mother had Wide local excision with right mastectomy Infiltrating duct carcinoma NOS(
Grade II BRS Modified) measuring 1.4X1.3X1 cm wit tumor metastasis to one of
seven axillaries lymph node with tumor size 1.4 cm size,Nipple areola, Deep margin , Free of tumor. Six cycles of chemo and tamoxifen taking. No radiation taken before or after surgery.

Due to the suspicion of malignancy, she was planned for wide local
excision followed by frozen section. Wide local excision and frozen was done
and was reported as infiltrating ductal carcinoma and posterior margin was
involved. So modified radical mastectomy was done.

After completing the last follow up with doctor two weeks later she started
having cough with scanty expectation breathlessness and left sided chest
pain it last for another two weeks. She went to a doctor and he did some
clinical testing like CT scan and chest examination and confirmed the
metastasis spread to lung and small lesion in the liver. Lung almost right
full and left 3 forth was affected. She went her regular doctor oncologist
and they did some pulmonary medical support for 10 days during their
investigation later she was given Inj.Docetoxel one dos. Later discharged
from the hospital and after within ten days she passed away.

The surgery done two and half years back.last one year she used to have tamoxifen.

please advise is this treatement  was ok for her. what could be the reason  that she could not prolong her life.After the metastasis to lung and liver she had 15 days left to treat.The oncologist were not sure how much area was invoolved in the lung cancer cells because they were suspecting the TB, and confirmed the spread bur said can start treatment only after TB test.

Was this treatement given in the begining for  Ductal carcinoma is currect. Any mistake done during the follow up. During folllow up no chest extra and CT done in last one and half year . But altra and mammo done.

Please advice yours opinion.