I don’t know too many long distance runners with lots of fat.
She does look too thin but don’t most marathon runners look thin?
All marathoners are thin,like one of my sons,a daughter,and granddaughter.
Serious Marathon runners... not the folks who do it just to prove they can once or occassionally.. are almost ALL thin. Unless you are very very young, your knees cannot handle the amount of pounding that these guys put on themselves to complete competitively, if you have any serious weight at all..
Just go look at images of “worlds best marathon runners” and you’ll see, all of them are very very thin.
To do a marathon in 2:45 minutes you are averaging something like 9.5 MPH. And to be able to do that on race day they are running 100+ miles per week training... IF you are doing that, first of all your caloric burn is going to be crazy... meaning you aren’t likely to have a lot of excess body weight to begin with if you are doing that... but if you are, it sure isn’t going to last long. Secondly to do that many miles every week, unless you are incredibly young, your knees are NOT going to let you do that for too long, unless you are very thin.