I maternally incubated last year, and everything went very well. I had 6 eggs, and ended up with 6 hatchlings.

The only thing I did was after she laid I realized that the humidity seemed too low for incubation (it was OK for every day husbandry). So I changed her bedding to cypress mulch instead of aspen, and I would mist it a couple of times a week to maintain humidity.

As others have said, they've evolved to do it this way. A healthy female can do maternal incubation just fine.