Sorry to say I did not see any of her paintings while at the Art Museums in Mexico City, DF. This painter seems to have exhibits in different parts of the world and her paintings can be bought at art sales.
The national museum of art does not have any Martha Chapa work as far as I know.
Her internet page indicates that some of her work is at a the Museo Martha Chapa de la Biblioteca Universitaria "Raúl Rangel Frías" in Monterrey City (North east of Mexico).
There are temporary exhibits of her painting in some modern art museums in Mexico and other countries. In her internet site you can find out details.
Get quick answers from National Museum of Art staff and past visitors.