I have doubts concerning the right position of adverbs, so which sentence is correct:
She had only a few months of life to survive or She only had a few months of life to survive.
By the way it’s more common to say a few months of life to live instead of survive, but that is also correct? right? Thanks 
I would avoid the word “survive” in this context. The meaning would be clear to all speakers, but it sounds odd, not native, and a bit morbid. The “of life” phrase would be optional. “She had only a few months to live” would be enough and is the typical way of saying this.
Actually the first one is correct, but most people say it either way.
I am a native English speaker - a LOT of native speakers mess up the word ‘only.’ It needs to be right next to the word you want to modify.
Here is the example that helped me learn it:
Only she told me about her raise. (no one else told me, only her)
She only told me about her raise. (she told me, but nothing else, for example, she didn’t prove it)
She told only me about her raise. (she didn’t tell anyone else, just me)
She told me only about her raise. (she told me about her raise, but didn’t tell me about anything else)
She told me about only her raise. (for example - she didn’t also tell me about her added responsibilities)
She told me about her only raise. (she got ONE raise)