My youngest was super fit, training twice a day everyday for her chosen sport, and generally competing at most sports at school to a fairly high level.
She knew there was a danger when the training slowed up that she would gain weight, but her habit was to eat big meals, and that habit was hard to break.
Over the past fifteen years she’s gone up and down, and to be fair, when she sets her mind to it, she looses weight really well , she looks young and pretty, but then it all goes back on.
I don’t mention it, try and be supportive, but nothing I say will have any affect, it’s got to be the right time for her.