This is a commentary for those who have not yet cleared "sasami".
The way to capture her is to attack the tongue as much as possible. If your tp is 75 or more, attack her uvula with a special attack 〚echostrike〛 (I don't know if the name of this special attack matches). And keep doing that pattern until she gives you the last warning!When she finishes muttering the warning, you just keep attacking your tongue!
At least if she's scraping her HP and not being swallowed by her, You'll succeed in capturing her!
I hope it will be a helpful commentary for you and other players!