Because she'll definitely listen to that when her best friend is in danger.
And a set of demons capable of warping space are definitely going to be tied down by a physical restraint when there's already an obstacle in our line of fire.
Not to mention that our initial response to any attack by Botis is to get out of the way and hope Matoko listens to us sending a trained professional demon summoner to play messenger boy.
Otherwise she gets hit and injured, thus taking her off the board in a shit ton of ways both now and in the near future
This plan isn't solid, it's incredibly reckless and puts two incredibly important charactera assets at risk. If it fails, Amu will not only have to deal with the seal on her own, but Hotsuin as well.
There's consequences to this approach if it goes south. And they are really bad for our position in the,setting. Especially with Comp. 5