She finished a bodybuilding show. That means months of structured dieting and training to hold a very specific look for one day. The look is gone now and the weeks that follow are harder than most people expect.
Her weight goes up fast. That is water and food coming back and it is supposed to happen, though watching it on the scale still feels bad. She will be hungrier than usual, possibly for weeks, because her hunger signaling is catching up to the diet ending. Her mood may drop, since something that organized every single day for months has just disappeared. Flat, tearful, or short-tempered in the first two weeks is normal. She might want a lot of plans, or none, sometimes on the same day.
Ask how she is doing and ask about something other than her body. Invite her to things that involve food and let her decide what she eats without any comment on it. If she takes food, do not remark on it. If she does not, do not push. Say something you appreciate about her that has nothing to do with how she looks. Leave the scale to her and her coach.
Telling her she looked better on stage, or better before all this. Asking whether she is going to keep it up. Commenting on what is or is not on her plate. Asking when the next show is, since she has a date set before she makes that call. Telling her to relax and enjoy the food, which sounds kind and lands as dismissive.
If she seems low for more than a couple of weeks with no lift, if she is skipping meals, if her training looks compulsive, or if she is pulling away from people, tell her you noticed and encourage her to talk to her coach or a professional. If you are ever worried about her safety, call or text 988.
You do not need to understand the sport to be useful to her right now.