If I had to put money on it, I'd say Olenna is not getting out of King's Landing alive.

She wants to make sure Olenna is safe when all hell breaks loose in King's Landing.

Jaqen's last words to the Waif was to not let Arya suffer. The Waif wanted Arya to suffer which is why she gave her the gut wound. She could have easily slit her throat. Maybe Jaqen was testing the Waif as well.

Jaqen's last orders to the Waif was to be sure Arya didn't suffer. The Waif wanted Arya to suffer which is why she gave her the gut wound.