Herceptin monotherapy for breast cancer

Hello,
I am sorry to hear about her recent recurrence of breast cancer, as well as the complications accompanying treatment.
I have no knowledge about "black salve", so cannot comment on this specific issue. About the other recent adverse events: Post-op infection is an unfortunate but not unknown complication of breast surgery, and especially after re-surgery with suboptimal skin closure. Chemo leading to WBC drops is expected, and counts rising (rebounding) to high levels as a result of growth factors is also common. severe diarrhea following antibiotics could be in fact triggered by these very antibiotics. In any case, metronidazole is a reasonable therapy, and cultures should indeed provide a clue.
About your question about safety/efficacy of chemo-plus-Herceptin versus Herceptin alone: I would suggest that first an evaluation of ER, PgR, and HER2 status in the recurrent tumor be performed (if not already done). There is often a discordance between primary and recurrent tumors, and treatment strategy should be tailored to biomarkers currently expressed on the tumor tissue. If she is still ER-positive, then hormone therapy can be considered (the exact hormonal drug to be given should take into consideration previous hormone therapy received (if any), and menopausal status). Chemo can still be cautiously restarted, with secondary prophylactic measures in therms of antibiotic and growth factor support. Anti-HER2 therapy must continue to be part of strategy if the recurrent tumor is HER2-positive. A consultation with the radiation oncologist should be taken for evaluation and advise.
I am not sure if I have answered your question specifically, but I do feel that there is not enough clinical information provided. Please feel free to ask additional questions, or request clarification.
All the best, and God Bless!