what could be wrong with this case

spacebmt

I have a question that my mother was diagnosed with breast cancer 3 years back T1N1M0, IDC, ER and PR Neg, Her 2 Neu Score1.She had Radical Mastectomy and given 6 cyles of chemo. Tumer messure 1.3X1.4X1CM.

Frozen Read: Invasive malignant Lesion= Nearest margin ( Deeper)shows tumour very close to inked surface. The adjacent breast shows focal areas of in situ ductal carcinoma componenet, adenosis,eithlial hyperplasia and microcalcification.

 She used to have Tamoxifen last one year.After the chemo over 9 moths later she had metastasis to lung and she died within three week. Can you please tell what was wrong with the treatment. No radiation was given prior or after the mastectomy. Doctor said chemo doesnt work. Please suggest the right advice. Thanks