Just start working her and it'll be fine. I would seriously hesitate touching anything about her food until after you start working her. This is from standing around doing nothing, once her energy requirements go back up, you'll be playing catch-up once again if you lessen her feed now.
I'm not sure what sort of "image" you're expecting from her but she may just be a thicker built Arab who's finally getting "there". My mare was narrow as all get out when I got her (obese though) then she lost weight and got even narrower so I assumed she was just one of "those". However, once I started getting her into more slow-long work and feeding her better (quality hay, high protein because she gets a potbelly when she doesn't get enough protein, etc), she seriously muscled up. She suddenly became this wiiiideeeee muscular machine. And I thought she was going to stay narrow! Hahaha
Of course, thinking that this may be a step in her fitness doesn't really include her belly but that's all probably due to the hay she's eating. The rest of her looks perfect. Finally not too skinny (imho, she's always been too skinny before this).
My other thought is that since she was starved for so long, it has probably taken quite a while for her body to build back up it's internal stores. If I remember correctly, she's only been out of starvation "mode" for about a year and half, so it stands to reason that her body may be finally catching up and finally able to get some fat on her bones. It does take about that long for some muscles in the body to rebuild after loss.
Fabio - 13 year old Arabian/Lipizzaner gelding
Hazel - 14 year old Angora goat
Atticus - 4 year old LaMancha/Alpine cross goat
Rest peacefully, Lacey.