Hehe... the OP is really filial. What's important when buying things for parents is the thought. I think as long as you give it to your mother-in-law, she will be very happy. For example, you can buy a health care device for the elderly. I think it's good to buy a footbath with massage and constant temperature function. Let the elderly soak their feet at night to relieve the fatigue of the day, which is good for their physical and mental health.
You can also buy some jewelry for the elderly, such as gold earrings, jade bracelets, and necklaces with magnetic properties that are good for health. These are all good gifts. They express your thoughts and are good for your parents' health.
In addition, you are not on a business trip, so you can consider buying some local specialties for the elderly so that they can taste the new things at home. The elderly will definitely be very happy. I hope my suggestions can help you.