You're definitely doing the right thing by getting a second opinion. It will give you a better sense of whether there are other options and, if so, whether those are options you Mom is willing to pursue. When you're stage IV, there does come a point where the treatment is worse than the disease and every patient has to decide this for themselves.
One thing that I would suggest, and it's difficult to hear, is start talking to your Mom about what she wants at end of life. It's not to say she's near that point, but research shows it's much better for people to talk about their wishes sooner rather than later. As disease progresses and people are under greater duress it because more and more difficult to talk about openly and honestly. Talking about it doesn't mean anyone is giving up, it just means you're putting a plan in place that reflects your Mom's values so that, when the time comes, you know what she wants and you can honor her wishes. Research also shows that one of the most difficult things family members experience is the conflict and grief that comes from not knowing the wishes of their loved ones. There are certain decisions you probably would not want to make for your Mom. Having these conversations, as difficult as they may be, will ultimately be a blessing for your entire family. Even if your Mom were to live another 40 years, end of life care will eventually be an issue. Talking about it, updating preferences as beliefs may change, these are all things that will bring peace of mind.
When my Dad was first diagnosed he was too sick to share his preferences. We spent the first night in a complete panic because we had no idea what to do. Then, after he survived surgery, we spent several weeks waiting to be able to talk to him because he had to have a trach. His condition was still touch and go and we still didn't really know what he wanted. Once we started talking, it was a tremendous relief to everyone, not only to talk about what he wanted, but for all of us to share what we would want individually in the event we were facing end of life. Everyone wants something different so it's important to let everyone choose what's right for them.
You might find this website helpful: http://theconversationproject.org/
Like I said, you may not be anywhere near end of life, but it's really never to early to start talking. As a result of my Dad being sick, we got plans in place for our whole family. You never know when you might need it.