I wouldn't say she's too fat - she's not cresty or big apple bum. The big belly will be a grass/hay belly- has she had access to lots of older long grass recently? My 2yr old has a similar belly but his ribs are easily felt.
I would say they look a tad overweight. It's always better to have too little weight on them than too much as the extra weight can seriously affect their growth. Most yearlings/2yo have pot bellys but as long as you can feel their ribs.
you cant see it in the photo but i can feel her ribs i thought she had worms but have worm counted her and wormed her she is all clear. i have just moved yards to sumwhere that hasnt had horseson for a long time so lots of grass and shes in a little paddock so they dont get too fat but its still quite rich