@wlittle6 Thank you for sharing this question. May God give you wisdom and may He give your mother-in-law peace, hope and faith! One approach would be to share what the Bible teaches about suffering and then to share testimonies from people who have faith in spite of their situation.
1 - Here are a few key verses on suffering. Jesus makes it clear that we will suffer, but that he has conquered the world. Romans 8 makes it clear that we all ‘groan’ to have our new bodies - these bodies may be breaking down - but we have a new body in glory. Suffering and decay are part of this earthly body, but we will get a new body in glory. I Cor 15 also has a beautiful passage on how our current body is corruptible, but at the resurrection we will receive an incorruptible body.
John 16:33 - I have told you these things, so that in me you may have peace. In this world you will have trouble. But take heart! I have overcome the world.
Romans 8:18-25 - I consider that our present sufferings are not worth comparing with the glory that will be revealed in us. 19 For the creation waits in eager expectation for the children of God to be revealed. 20 For the creation was subjected to frustration, not by its own choice, but by the will of the one who subjected it, in hope 21 that the creation itself will be liberated from its bondage to decay and brought into the freedom and glory of the children of God.
22 We know that the whole creation has been groaning as in the pains of childbirth right up to the present time. 23 Not only so, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for our adoption to sonship, the redemption of our bodies. 24 For in this hope we were saved. But hope that is seen is no hope at all. Who hopes for what they already have? 25 But if we hope for what we do not yet have, we wait for it patiently.
1 Cor 15 - So will it be with the resurrection of the dead. The body that is sown is perishable, it is raised imperishable; 43 it is sown in dishonor, it is raised in glory; it is sown in weakness, it is raised in power; 44 it is sown a natural body, it is raised a spiritual body.
2 - Here is the testimony of Nick Vujici - born with no arms and legs. Perhaps his faith could be an encouragement to her. How many times do you think he prayed for God to give him arms and legs? Yet he decided to trust God with what he had and it is amazing to hear his testimony.