If IW is actually LW, then it stands for lightweight (similarly MW and HW are medium weight and heavy weight)
Can refer to rugs (refers to how thick they are) and horse type - especially cobs and hunters (generally refers to body type or how much bone they have)
I think the point OP is trying to make, is that whilst she is happy for her liveries to be her FB friends, she would prefer work related items to be send to her mobile and not via FB. Hope your message works OP!
Heehee, well I'd have guessed there was a *smidge* of Clydesdale in there :) He's clearly made his mark on your heart, whatever his background, and rightly so! :)