The issue isn’t her age. It is her health. My wife is closer to 70 than 60 and she is healthy, can do pretty much what ever she wants to, -could certainly fast if she wanted to.I know others in their 30’s who really shouldn’t fast.
Tbh, I dont mean to sound disrespectful of your situation but the sub is for people who voluntarily fast. Enforced fasting because you dont have any money is something entirely different (i.e poverty). I notice some responses that may be helpful but perhaps a different sub to do with poverty will be a better solution for you? (e.g r/EatCheapAndHealthy ) Is not even very cheap meals like beans and rice an option for you?
A secondry issue you may well face is when you break your fast, ideally you and you’re family (particularly your 70 old mother in law) want to follow up the fast with healthy nutrient dense foods to replenish any nutrients lost during the fast. If you dont do this you’re setting yourself up for malnutrition(especially if you and your family dont eat particularly healthily previously). Unless I was overweight (Im not btw) I wouldnt fast if I was unable to do this