Unfortunately it can be very serious, thankfully as they have identified it early they can put the support and processes in place which helps to manage it, so hopefully all will be okay for them. I think it's brave of her to post about it tbh, so many on social media just post about how much of a breeze they are finding everything, and it can be hard to find support when things aren't. Anything that raises awareness and might give someone the confidence to reach out for support if needed is good, and I really hope she is doing okay, it's a lot to process, especially when you have never heard of it before!
Also nosey about the money situation haha, I'm guessing their parents might be okay for money, as she said they grew up in a 5 bed?