Pretty much yes - you get sick and train up your immune system
Often kids will catch every little thing for about 2 years when ever they start going to daycare (or when I was growing up when we started kindergarten).
Then things usually settle down quite a bit.
Can she fight the flu off?
Hard for anyone but her doctor to say - and sometimes they can't tell either.
Flu can vary quite a bit depending on the strain.
For some it's no big deal but for others it can be life threatening.
Anti viral medications can only do so much - but often it's a secondary bacterial infection that's more dangerous - but antibiotics can help with that.
Hope your friends daughter gets better soon.
Our son had RSV and pneumonia at 14 months old.
It was hard keeping up with the meds and nebulizer but I stayed with it and kept him out of the hospital.
Doctor said I saved his life.
Ever since then we've all got our flu shots every year and kept up with pneumococcal shots too.
Additional:
When my sister and I were kids we stayed home until kindergarten.
Once in school we got sick with everything that went around for about 2 years.
I can remember going to the nurses office and throwing up all the way down the hall.
After those first 2 years it settled down to getting sick only a few times per years.
When our son was born he started day care at 3 months old - and for about 2 years he got sick with everything that was going around - and then it settled down to only a few times per year.
It's just an observation - but it seems like it takes 2 years from when kids begin a more public exposure to germs before their immune system can really start fighting off catching colds all the time.
Any time you start a new job - or start working around kids - like in a daycare or school - new employees have a few months where they are a little more sick than usual.
In the office I worked in we had a guy whose job it was to go around and apply updates to all the desk top computers.
Every time he did it - touching all those keyboards - he got sick for a week.