Primrose You know your mother better than any of us. Some people are old at 70, some are young, some are fit and like to go out and about, some have mobility problems or prefer their own fireside, some do all kinds of crafts, some never could thread a needle, or their eyes and fingers are not now as nimble as they used to be.
How does your mother spend her time? Does she read, knit, sew, garden, go out to clubs or classes, volunteer? Does she see her children/grandchildren often or live far from them? Does she enjoy a meal out?
If you answer these questions, and think back to what she enjoyed doing when she (and you) were younger, maybe you can think of an answer to your own question? If you are still stuck, i am sure people will come along with plenty of suggestions.
One thing that is certain - she will appreciate your company doing something together.