A very warm welcome to our forum.
I'm sure that you're feeling pretty shell-shocked at the moment, but DCIS is about as good as it gets. It is eminently treatable. I was diagnosed with this 12 years ago. I has a second bout the following year and had a double mastectomy and, have never looked back. I still lead a busy and fulfilled life. At the time I was worried for my two teenage children. Since then I have seen them leave school, go to university, graduate, find gainful employment, marry and produce two beautiful granddaughters, who are the light of my life.
Once you have had your MRI they should be able to tell you more about the size of your lump. You have been through a lot recently, but I am glad to hear that you have the support of your sister. We all need someone to confide in with situations such as this. As you know there are no guarantees with cance, but then there's no guarantee when we are crossing the road, yet we don't think twice about that.
It will be a great help to your future if you can remain positive about this. Breast cancer is one of the most treatable forms of cancer. Yours is in the early stages and, it is treatable. Hold on to these thoughts.
Please keep in touch. We sre always here for you.