She is decent sized for an April foal, but I would definitely be concerned by the fact that she is on the thin side. I would be deworming her, or at the least getting a fecal done.
As far as showing, are you planning to show this winter? If so, I have horrible news for you; you will have to body clip her, as the Arab world is a very tough show world...if she's not clipped, you may be docked severly... She looks like she has decent conformation under all that fuzz...I would try something like Grow Colt, or Calf Manna to help her gain weight, and conditioning. Start getting her used to electric clippers, as you will need to clip her bridle path, and whiskers, at the least, after she sheds out. Unless, like I said, you are planning on showing this winter yet.