tech companies and security experts say that if an encryption backdoor is created it will be impossible to ensure that only the "good guys" use it, and so effectively undermines the whole system.
Correct for an end-to-end encrypted system. Incorrect for a store and forward encrypt-to-provider, encrypt-from-provider system.
She cannot do anything against physical persons and corporations using end-to-end crypto themselves. That horse has bolted 20 years ago when Phil Zimmerman gave PGP to the world.
Now, provider assisted is a different story. She can do that TODAY.
The law as it stands is an ass and being a dumb ass it does not give a flying f*** about the application design disallowing legal intercept. It insists that legal intercept is provided and the way it is formulated in half of the Eu allows the law to take a big hatchet to any provider-run end-to-end encrypted messaging (once again - it cannot do anything about private persons today). By the way, by disallowing USA corporations to take any cases with them to California, Eu has already done half of the work on this one. The remaining half is a court case which will happen sooner or later (when someone finally explains the retarded politicos that the law has already taken care of this).
So all it takes is ONE court case to prove that legal intercept requirements apply to Facebook, Google, Telegram and friends. We will be back to using PGP in email on the next day after that.
So, in fact, she does not even need to legislate. She just needs to pick one of the Eu countries to start the court case.