No, there is no risk of permanent damage. You can plan your mother's visits for the cooler time of year there, too. For example, I spent 6 weeks in the Philippines, over January into February (which was their cool season), and suffered no long-term effects. I was glad for the air conditioned hotel that we stayed in, and the air conditioned car we rented. And there were a couple of days when I let my husband go out and about and I stayed in the hotel...but
generally I had a good time, saw a lot of the country, ate some lovely food, met some lovely people..generally did well.
You could plan to carry cool beverages with you if you sightsee, and I took a neck band that I could dip into cool water and wrap around my neck, and a scarf for my head that I'd get wet and lay on my head if I did get too hot. I find that if I'm overheated, once I get cooled back down (like getting back under air), I'll be fine. I think that'll be your mother's experience too.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....