Arabians also develop later.
One of the leading endurance mares in the breed has logged over 3 thousand miles at the age of 7 and gotten best condition numerous times finishing in the top ten.
She was bred at 2 and foaled at 3 without any adverse affects.
As long as that mare has received good nutrition she will do fine. Im not advocating breeding one at 2.
Your points are valid reasons to be concerned. Hopefully the OP will see mine as encouragement to ensure proper nutrition if she is bred. Shalom