Here's my 2cents.

I think this is better in an email than over the phone.
WW can hang up the phone as soon as she hears these words, and may not store them in her brain, or she can argue back 'well it's too late'.

Gerka is not around to remind her daily that he is committed to this M,as would the typical Plan A scenario work.

Written in an email, one that WW could reread over, hearing the words in her head and also seeing them in print.
Mind you, she could also delete the email, but I don't think she is deleting them, I have a hunch that she is holding onto them.
Could be wrong.

There is nothing confrontational or relationship talk with this reply.
WW is the one who spoke those words first, I think it is wise to use this window, or reply to the bone that another poster referred to.
He is only stating a fact.
It doesn't require an answer, simply let's WW know where Gerka stands.

Like I said, just my 2cents and wanted to throw this out there as another POV.