Isis is the best because she has the best economy for affording Elephants with her unique God tech Flood of the Nile trickling Food and Prosperity God Power boosting Gold income along with her bonus of +5 population with each Town Center you have and with Bast Classical Age up choice the Sacred Cats tech boosting Food income.
You can advance into the Heroic Age with Nephthys for Nebty tech for more health on Priests and Pharaoh to keep them alive longer to heal Elephants and with the tech Spirit of Maat which makes your Pharaoh and Priests which are cheaper to train also heal faster. You have Funeral Rites tech which gives you back some Gold when your military units dies to help sustain Gold economy for making more and more Elephants.
You can advance into Mythical Age with Thoth for the Book of Thoth tech to boost your economy and Valley of the Kings to make you get extra Elephants trained from Migdol Strongholds that are Empowered and then Tusks of Apedemak tech making your Elephants cheaper in resource and population cost as well as stronger in combat.
Bonus: Town Centers and Citadel Centers support +5 population.
God Power

Target anywhere to make all of your Villagers and Trade Caravans gather Gold faster.
Isis ensures the continued fertility of your lands, granting a steady trickle of Food.
Bast’s cats protect Granaries from vermin, improving all Food gather rates.
Nephthys increases the healing rate of Pharaohs and Priests, and lowers the cost of Priests.
Nephthys increases Priest and Pharaoh hitpoints, as well as their damage against myth units.
Nephthys compensates you with gold when your warriors fall in combat.
Thoth makes War Elephants stronger, cheaper, and reduces their population cost.
Thoth teaches secrets that cause Barracks and Migdol Strongholds to spawn additional units when empowered.
Thoth’s secrets allow your Laborers to gather Food, Wood, and Gold faster.