Is this emotional blackmail?

So my mom is not very steady on her feet at all. She does decently around the house, but walking in the grass is a whole other issue. She takes her cane with her, but she is very unsteady.
I have heart issues and am not supposed to be out in the heat of the day. She waits until today when the heat index is supposed to be over 100 degrees and there’s an air quality alert to say she is going to go out and weed her gardens (in the heat of the day no less).
The last time she went out back, she ended up falling. No major injuries thank goodness, but it could have been a lot worse.
Now I’ve told her I am not going out with her in the middle of the day, due to my own health issues, and that she should wait, but she insists she is fine to go out. She’s 81, by the way.
How would you handle?