I think she really should have a breast collar, so she learns to pull into it.there shouldnt be any weight on her back at all, and when you get to fitting the cart it must be balanced so there is no weight in that area. Therefore, not really much point in attatching anything to the surcingle. And the "shafts" as mentioned before, should be wood. Yes she needs to feel themalong her sides, and learn how to turn with them, but if plastic piping breaks breaks, you could end up with a stabbed horse. Almagron N; agree about the difference in terminology between uk ans usa, ie. The wheel, but I use a wheel, meaning the entire metal center with the rubber tyre included. Just the rubber trye is not heavy enough, and get scaught up to easily in rough ground, or turning over. So I use a entire wheel or a one half railway sleeper....also jimmy has given a good suggestion ie using an old seat belt to make a breast collar, if you don't want to buy one, but I would pad it out, very carefully to prevent rubbing, and also get the real thing as quick as you can; synthetic are cheaply bought,or buy secondhand.