But creating legislation that bans the use of crypto would be within her powers.
Actually - no. Crypto nowdays is math, an Eu commissioner is not the Indiana legilsative, it cannot decree that Pi 3.00.
What she can decree and what she can refine the requirements towards providers for legal intercept to make Telegram, iMessage and Facebook chat in its current form illegal. That is perfectly achievable technically and that is something a politico can and should do.
She may try to also specify reqs to commercial software, but that is going to die on technical grounds long before it gets anywhere near becoming law.