It is not just that - what was her emotional health like?Was she able to set healthy boundaries or not? Was she emotionally abused by others and did she allow that?
How was her stress level in general?
I am saying this because my mother died of a brain tumor in 1991. Her younger and older sisters are still doing great. The biggest difference between the three is that my mother was emotionally abused by my father who is a very controlling, intolerant physically and verbally abusive person, while her siters are both in loving and supportive relationships.
Now in hindsight I believe her disease was caused by the constant stress that my father created and she allowed it to occur. There was no significant difference between her and her sisters lifestyle or diet otherwise.