My prayers and thoughts are with your girlfriends sister.
4 months is a reasonable amount of time, but you will have to act fast.
You need to find out all you can about sarcoma of the lung, and what seems to help. Check into both conventional and alternative treatments. Miracle-Mineral-Supplement is an oxidant. If you find any cases where oxidative treatment was beneficial, then an aggressive use of Miracle-Mineral-Supplement may be considered.
You can organize a small group of people. Have a couple looking at conventional treatments, another couple looking at alternative treatments, and a separate person organizing the findings. If you can manage a meeting every third day or so, you should be able to concentrate your efforts in needed areas as well as getting a feel of how things are progressing. Your girlfriends sister should take part in these meetings.
The idea is to find something, or a combination of somethings that will slow down the spread of the cancer, and this will buy you more time.
I don't know if Miracle-Mineral-Supplement is the best "first line" something to use. You will also want to look into antioxidants like vitamin C. However, MMS may be able to help if your friend has other health issues.
While you are trying to figure things out, my recommendation is going to be different from most people. I think you should consider a pulsed approach. If you take MMS for 4 days, and take antioxidants the next 3 days, and repeat this, I think you can get the maximum benefits from both the oxidant and antioxidant approaches.
Until you know that an oxidant approach is the best way to go, I would strive to optimize the MMS dose, and avoid the possibility of creating additional discomfort through nausea and/or diarrhea. The best way to accomplish this is through a modified activation method, and by not trying to rush into things.
A very comfortable, yet still very powerful solution, can be made by using 10% citric acid as the activator, and putting 3 drops MMS into a glass, add 1 ml water and swirl the glass to mix things up. Then activate with 1 ml of the 10% citric acid , and wait 10 minutes. Dilute with 500 ml of water and this solution is sipped over 30 - 60 minutes.
This activation method is designed to minimize the amount of ClO2 that is released during activation, which leaves more in the solution to work inside the body. In tests run outside of the body, this solution has the same effectiveness as a 5 drop solution activated according to the MMS protocol. Unfortunately, no one knows what happens inside the body other than in some cases it seems to help people.
This solution will not have a strong taste or odor. If improvement is observed, you can mix up a dose in the morning, and another in the evening.
If you find that oxidant therapy is the best way to go with this cancer, then you may want to consider a "chemo" approach. A couple of strong doses a few hours apart followed by a few days to recover.
I think it is very important to keep a journal. When you get down to the wire, this can keep you on the right course. I also think it is very important to keep the doctors in your loop as well. They may not approve of the alternative treatments you come up with, but by informing them of what you are doing, they can keep an eye out for any adverse reactions.
Please understand that I have no "formal" medical training, and that this is my "best guess." I wish I had more that I could offer you...