Depending on how far back the miles have expired, she might apply for a re-engagement challenge. I think it was $30 or so, and she had 2 or 3 months to fly on AA/US and credit to her account in order for the other miles to be re-activated. She also needs to sign in to receive emails from AA as well. I checked AA.com and do not see this mentioned, not sure if they no longer do this, but I did this last June on behalf of a friend of mine who lost about 25k miles, she managed to get 18k back. Might need to call AA and check on this, also you need to take in consideration if your grandma will travel.

Is it worth it to pay the money to activate it? Only you can answer this question. Will she be the one using the miles? maybe some family member could certainly take advantage of an award trip on her behalf. If that is the case, then see how much a "dream" trip would cost, then see how much it will cost in miles, who knows, it might be worth it.

75k miles can get you almost 2 award trips to Europe in Mile Saver Economy, or 3 domestic trips in Mile Saver Economy. Personally, yes, it is worth it if you plan to make use of it.