The article notes that cetaceans and primates are the only mammals known to provide assistance during birth.

I would also have expected elephants.

Anyone know more?

During birth. Elephants help after birth. Horses help after birth. All these herd animals will stand and watch during birth and help after birth.

Maybe? The article only seems to note buoyancy assistance for the mother whale - not that whales have prehensile tails or anything, to do a lot more.

Vs. elephants have trunks. They normally use those to handle their young. The action barrier for an elephant matriarch, observing that another elephant is having problems in the final stages of delivering her calf, is very low.

Maybe you're right, and it just doesn't happen? But it seems like you'd need a lot of closely observed elephant births to establish that fact.