I've been such a long time lurker on this thread but finally had to post something !! (Sorry for the long post lol)
I can unfortunately relate to Holly's story in many ways, I too suffered from an ED in my late teens which I am still recovering from (am in my early 20s now so was recovering during uni etc.) and lost my period which I am yet to get back. What is mind-blowing to me though is how little support her parents gave her, my mum marched me to the GP who immediately referred me to CAMHS and I had weekly therapy sessions. Unfortunately how or if you recover hinges on your personal attitude and to some extent you have to take responsibility for your own recovery, I was threatened with inpatient but managed to stay at home, do my A-levels, go to university and recover on my own and with my mum's support, rather than just pretending that I didn't have a problem.
I also became vegan in my recovery (like loads of ED sufferers as it's a great way to restrict sadly) but the difference between our diets is staggering, I eat an abundance of carbs, fats (not just a tiny drizzle of tahini), protein etc. and eat 3 meals + snacks everyday, also don't claim veganism *cured* me haha. I also exercise way less than Holly (basically just walking and yoga definitely no running or HIIT etc.) yet I still don't have my period back after many years in recovery and restoring my weight + higher body fat% than Holly based on looks. I find it hard to believe from looking at Holly that she has her period, I'm not suggesting that she is lying but sometimes people get their periods back when still underweight (I think it depends a lot on the individual) and mistake it for a sign that they are healthy and can continue as they are. I worry a lot about the health impacts of my ED so it blows my mind when Holly shrugs off the risks of low bone density which don't just end when your period returns, she's had years of no period (like me) which is a crucial time for building up bone density so she is still at risk of osteopenia/osteoporosis, so doing a marathon without fuelling herself properly or even checking her bone density before starting her training programme just seems insane to me.