Also I forgot to mention..heat not only can effect the starter but the cables going to it.
Less amps are delivered when wires get hot, and aging smaller diameter cables can be refreshed with an upgrade, to provide way better power delivery.
It may be worthwhile to consider replacing the cables with a thicker gauge wire.
Check the wires closely, inspect for wear and terminal ends. Use 2ga if you feel a replacement is necessary.
I recently used Anchor Marine tin copper wires that I made for the back of High output alternator to an Odyssey battery in 2 gauge..nice quality and mega power under the hot zone.
How many CCA is your Mom'* battery rated at? After a load test ....see how it does... Many of the GM cars came with only 640 CCA when in new condition.
When time comes to replace the battery look for the most CCA you can fit under the hood like 800CCA or better!!! That will be better in the Arizona heat wave too.
Still nothing beats an odyssey battery!
ODYSSEY Batteries - Auto and Light Truck
From midtronics load tester..1219 CCA!! that might crank your starter over with ease even when hot!