Firstly, without more info, can't say why she's tender sorry. However, it could be the trim, could be that she's not conditioned for rocks, her feet aren't healthy & strong enough, could be diet, lifestyle, etc. With pics & further info we may get a better idea, but even then, don't think it's fair to question a farrier's work if they're chipping when they're due for a trim - if not maintained frequently, by 4-6 weeks most horses have at least a little deformation of the hoof walls.
What does sound a good idea tho is getting boots for her, as it's important to provide enough support & protection to allow a horse to exercise in comfort, aside from avoiding possible injuries through lack of protection. Again tho, I would not bother measuring her when she's due for a trim, but immediately after a *well balanced* trim. The biggest question when choosing boots is the best fit for the horse in question, I reckon. Therefore having them first would be helpful, because it may rule out some options.
The Easyboot range are generally pretty good, and while Gloves are great, hooves need to be in very good form for them to suit & fit properly. I also would be cautious about buying before trying them, as the sizes are more precise than other boots(you can order a 'fit kit' to try before buying). This also means that for good fit, you'd also probably need to trim more than 4-6 weekly - brush ups in between for eg. Epics or such are more adjustable so a bit more leeway size-wise and having a fastening system like other types, don't need hoof form to be so perfect to fit well. High profile boots such as Old Macs, the new Easycare Trails, etc tend to be better/more secure for jumping. I'm not sure that any boot is actually designed for activities such as jumping though.