[SJT15]

As-Salam-Alaikum,
I am in a terrible predicament right now and I seek help. Islam seems to be the only thing that has been helping me all along and right now, I cannot possibly think of anything better than to ask for it's help again. I am a 16-year-old girl from Bangladesh and I am a Muslim. I pray regularly but it would wrong of me to call myself an ideal Muslim. I try to follow all the rules which Allah has given me the strength to follow, and I am working on improving myself in that regard.My mother has been very ill for quite long now and I have been praying for her recovery all along. Alhamdulillah, Allah has granted me a lot of what I had wished for since she is feeling much better now. But recently, she has been feeling sick again. Her doctor says that there's nothing more he can do. What do I do? Is there a dua which I can recite in order to make her feel better? How do I pray to Allah for her recovery? Everything I do makes me feel guilty, like it's my fault. Help, me. I am in desperate need of it.
Jazakallah Khair for your help.