If it was me, I would definitely go for it. I have researched RFA a lot and I deeply regret not insisting that my mother (also mets to liver and lung and just started erbitux/irinotecan) did not have it prior to starting chemotherapy. From what I have read, combining RFA/chemo has a better outcome than either therapy alone. yes there are side effects but death rates are .4 per cent or roughly one in two hundred with the procedure. Meantime my mum's cancer has progressed so now it is no longer an option.
As you say, your mum is running out of options.
I wish you both well and I would love to hear how your mum gets on.