It all depends on the mare. Every one is different. I've had one mare that resembled her, belly wise. Most of my mares had BIG bellies and were very predictable. VERY textbook.do you think she is small to be late term pregnant? I have upped her feed to 1/4 scoop of mitavite breeda (which is an aussie brand pellet for pregnant and lactating mares and foals...) its about 17/18% protein?
Your feed should be okay. I know some countries don't have the same brands as we do, but a higher protein percentage is good. I fed my mare 16% protien and she did great with her baby nursing. I fed it to her pregnant as well. It helped her gain the weight that she needed.