I have shires (adult) synthetic suede half chaps that are now about 9 years old and have stretched out a bit now but not much. I would say if they are uncomfortably tight then she needs the size up as they won't stretch out that much. If they where real leather ones they might stretch a bit more.
Very dull,but I just don't know the answer.My mum bought DD1 some new half chaps in medium as her small ones were getting tight.However,we really struggled to get them on and DD1 had to remove them half way through the day on Sunday as they were too tight.
They are Shires elasticated ones and I'm wondering if they stretch and give a bit more with wear.We have only had hand me downs before so they were well broken in before they came to us..DD1 is tiny and very slim,so I can't understand why medium won't fit.