Given that your grandmother is 88 years old with oxygen-dependent severe chronic obstructive pulmonary disease (COPD), her risk of any type of surgery will be high, especially with a major
procedure such as fractured hip repair. Her aortic aneurysm is relatively small at 3.5 cm, I assume you meant cm and not mm, and poses minimal risk.
The first thing you should do is to have a frank discussion with your grandmother about her desire for surgery.