Worriedd - I'm so sorry your wife is going through this, - you are absolutely right, the waiting is the hardest part, - I speak as a breast cancer patient myself.
If she is Dx with BC, then what you probably need to know is what path her treatment will follow, probably initially surgery, then the results of the surgery will determine what happens next. (Occasionally people have some chemo before surgery to shrink the tumour.)
Not everyone needs chemo - it depends on the size of the tumour etc. some people have surgery then radiotherapy and possibly tablets afterwards, depending on whether its a hormonal cancer or not.
There are several different types of BC, and what type you have will obviously influence the type of treatment you have.
Take a pen and paper with you to the appointment so you can write things down you need to remember. Your wife will be assigned a breast care Nurse who will be an invaluable source of information and support - they really are wonderful and you and your wife can phone her and ask whatever you need to know or are uncertain about.
YOu are often bombarded with leaflets and info. - which can be hard to take in when you are feeling emotional an bewildered. So take your time to look through it all when you get home.
I do hope everything goes well for your wife and I wish the very best, I can say from experience that once the initial shock of diagnosis has passed, you may both feel calmer because you will know what you are dealing with, and your DW will be starting on her treatment and on the road to recovery.
Breast Cancer Care is a good informative organization (just google the site) and they also have helplines you can phone.
There is a thread here on health for people with breast cancer - we are all at different stages of treatment and recovery and have a fair amount of experience between us. Please do pop onto the thread and ask questions - you will get all kinds of help, and everyone is welcome patients or family for support 