I'm very sorry to here the news but I can understand the need to do something when you feel helpless to a situation.
I was a nurse and as such I followed convential medicine however quite a while ago (and I know this is not actually related) but quite a while ago I had a dog who was diagnosed as have chronic renal failure and she was basically very sick, although she didn't look that way. I was given a herbal book by someone in the family, I, in desperation decided to try some infusions from the book and as we had to go back for blood tests every 4 weeks I know I have proof because the blood tests can't lie, but anyway her creatinine and urea levels were off the scale, 4 weeks later following parsley and honey infusions twice a day and a low protein homemade diet (vet wrote out for me) her levels for both had halved (still high, but halved). The vet was amazed and said the diet alone could not have done this. She told me to carry on. You can't cure CRF but it can be managed to prolong quality life which is what happened to my dog.
I now look very differently at herbs and when faced with such a dilemma there is nothing to be lost by trying such things.
Firstly I have to say there is currently no treatment cure to metastatic breast cancer, but herbs can play a part in the whole treatment options.
Increase selenium, Vit E and Vit C, intake
If she's well and has been active encourage exercise and activity still
Start echinacea to combat infection and boost powers of resistance.
Use multivitamin supplements and zinc.
Try to add garlic to the diet.
Reduce the amount of refined carbohydrates that are eaten as cancer thrives on higher sugar diets but still allow simple sugars ie honey or other natural sources found in foods.
Flaxseed oil has also shown to be helpful and can be added to diet.
If cachexia (severe weakness and wasting) use dandelion infusions to stimulate liver and assist metabolism also used fenugreek seeds (must be soaked overnight before being used). They have a slight curry smell to them but are good at increasing weight.
Now herbs that have shown to be very useful with cancers especially breast cancer are wild violet leaves (these can be ordered in from a good herbal shop, even a high street one). This is the website too of a herbal shop in chorley that I ordered them from it was a special order but they did get it for me
www.yourhealthfoodstore.co.uk tel 01257 276146
Other herbs that have been useful and you will be able to get off the shelf. They are dried and come in small packages and are all very cheap as opposed to tablet form are Burdock root, clivers, comfrey, there are others but these are a start.
All herbs are made into infusions and are given at least twice a day. No herbs mentioned are harmful and can all be given along side conventional medicine.
If you want to try the infusions I can post how to do them, but they are simple. Otherwise they all come in tablet form.
Fresh grape juice is also very effective as a treatment.