The sad fact is that women put up with health problems for years and just get on with life
She might have endometriosis and be in agony on and off, she might have a prolapse that she's had since birthing her children, she might have incontinence after carrying children, she might have IBS or crohns etc. She might bleed very heavily every month, who knows? Very often women put off seeking help for these conditions. She might have a huge boil on her arse that needs cut out and packed, they can take months to heal and recover from.
Yes she will have access to the best of the best healthcare however it doesn't mean she chose to confide in someone about a problem, maybe she's kept going for a few years as many other women do.
Being slim young and fit doesn't mean these things aren't happening. I'm still thinking hysterectomy or prolapse repair given the time frames for hospital and recovery.
I do understand her wanting to keep her medical issues private however they must have realised how much speculation their statement would cause.
Its a shame that whatever it is, she feels the need to keep it hidden.