There is some really great advice here already and I will try not to double up. Some small tips from my experience so far. I am in Australia and have Her2+BC Stage 3.
My husband followed instgram women with the same type of cancer as I had from all over the world + researched different treatment options/recent studies online prior to our Oncology appointment. My mind was not in the right place to do any this for myself after diagnosis. This helped me as he seemed to know and preempt what I might be going through during chemo and had his own questions for the oncologist and surgeon too.
Through his research he found a drug that gave me a higher succes rate of PCR. This drug wasn't offered or even mentioned to me in the public hospital in Australia so I chose to pay for a second opinion. I am know paying to go to a private hospital/oncologist to get the best treatment regime for me. I wouldn't have known to ask about this drug if he hadn't have read about it and I would have been on a completely different regime funded solely by the PBS.
SIDE NOTE - I'm not saying you shouldnt trust your medical team. You should trust your oncologist as this is their field of expertise and they will be working hard to get the right regime for you based on your wife's diagnosis and their available resources but please also be aware of your own options. The system isn't always foolproof.
Health checks - Please make sure your wife sees her dentist so she can make sure her mouth is healthy pre chemo. My dentist also asked me to start using a fluoride toothpaste with a plate at night to help strengthen the enamel. I have very bad indigestion. I now have a softer toothbrush and have been using Oral 7 products and have not had 1 mouth ulcer yet!
If you have a bath tub - My husband lights a scented candle and runs me a bath to soak in on bad weeks. It is like a big warm hug + it helped soothe my scalp as my hair fell out.
Lastly help her get out of the house for walks. Some days even thinking about getting from point A to point B in the outside world is exhausting but staying inside can get depressing. Take the resistance away from getting out into the sunshine by planning little walks for you both or setting up a picnic lunch in the sun. Super helpful for her mental well-being as well as her physical well-being and excercise is shown to improve outcomes as well as reduce side effects from medication.