Daughter's weight gain

I love this group of gransnetters - think I rely on your advice more than I do my own nearest and dearest!

I have never been good at asking for help but I’m desperate for your input. My husband and I have two daughters aged 34 and 29 - we are a tight knit and supportive family and I communicate openly with our girls about all things - mostly!
Our younger daughter has gained over 4 stone in the past two years. She has been weighed at our local surgery to continue the contraceptive pill and told she is clinically obese and to lose weight?

My own mother was hyper critical of diet and appearance and both my sisters developed eating disorders Therefore. I vowed that I would never make critical comments about my own children’s weight ever, unless it was life threatening? We eat healthily and neither my husband, my other daughter or myself have serious weight issues.

I have always guided them about eating if they asked me. My younger daughter has ADHD and finds it difficult to organise her life. When she told me she was getting concerned about her weight, I suggested blood tests as she is a chocolate junkie. They showed up nothing. She is a cleaner/carer and walks to all her jobs so gets exercise but is finding it more difficult in the hot weather.
She has a very nice boyfriend who is in the army so she socialises with girlfriends a lot. She says he encourages her to eat healthily when she actually sees him.

I’m sorry about the ramble- I just don’t know how to help her in a subtle way without hurting her feelings. Do I just not say anything as she’s nearly 30 and doesn’t live at home but we see her often and she sleeps over with us once a week.

She has approached our doctors surgery for an appointment but they did
Not get back to her and she will probably lose initiative? She has low self esteem but I don’t know how to help her without estranging her?
Please help me gransnetters 🙁