I'm also 5'3" and started to see this as my weight dropped below 125lbs. I actually decided not to push down to my high school weight of 115 until I get some more lean mass, and maybe give my body fat some time to adjust. My arms are looking scrawny, despite some visible fat still around my middle. I agree that veiny forearms are not a good look. I'm hoping that taking it slow with the last 10lbs will help.
CW-125, part calorie counting, part transition to primal
GW- Goals are no longer weight-related