YTA

I would never have gotten there had I been overweight

Incorrect, you never would have gotten there without self confidence and believing jn yourself - for you, losing weight was just a vehicle to allow you to get to a better headspace that allowed you to succeed in your professional life.

she would fail me again

This is her personal journey, so I don't understand why you think any part of it is about you, or is a reflection of you, so this line is completely ridiculous and full of your own self-importance. She asked you for help, and you gave her help, but without knowing the specifics, we can't know that the meal plan you originally gave her was healthy, suited to her specific needs, or adequate for her schedules/work routine/etc.

Regardless of everything else, it's never cool to shame someone - losing weight is mostly in the mindset and trying to frame your headspace and perspective into something healthy, but by shaming people you're only reinforcing that currently negative hesdspace and possibly low self-esteem, making it harder to continue to muster up motivation. 'Tough love' in this form is toxic and damaging, and overall unhelpful and counter-intuitive