Where should I go with my mom?

Adventurous, full of culture and history, but not stressful is a tall order especially for 10 days. That really becomes 8 days when you consider travelling days. I would say Machu Pichu flying directly to Cuzco. Any extra days spent on the altiplano. Less stressful: Banos in Ecuador, flying into Quito and a short bus ride to Banos. Lots of hiking around there. Both places would be even less stressful if either of you spoke some Spanish???

Yes, Canada...you won't have to worry about jetlag cutting into your holiday. Ottawa, Montreal, Quebec City.
Or west coast...Vancouver, Victoria and maybe up island to Parksville or Yellowpoint(book now to stay at Yellowpoint Lodge) or across to Tofino or Ucluelet or a stay on one of the Gulf Islands for a couple of days.

How about going to the Galapagos?

When we were there last fall, there was a mother/daughter combo, and I think they had a great time. With only 12 on the boat, we all got to know each other, so they had lots of chance to spend time with other people, not just 24/7 with each other. The mother didn't snorkel, but she seemed quite happy staying on board. (she was younger than me - not an age thing, just not comfortable snorkeling).

Well, that reminds me---last fall I went to both the Galapagos (fabulous---you would both like it) and Easter Island. The later is a long flight but no jet lag, and the island is laid back, pleasant, and interesting with all the history there. It's cheap, if you want it to be. You can take small tours to the high points of the island, and just hang out in the village (pop. 9,000). The Galapagos would be more physically active; Easter Island would be less physical unless you want to do hiking or biking.