It would suggest the feet aren't very healthy, going lame after being shod 6 weeks would also suggest all is not well with the feet. Its very rare for a horse to be 100% fine and healthy footed in shoes and be lame without shoes on soft ground, but going lame after 6 weeks indicates all is not fine even with shoes.
Its less likely than on lush grass, but just not enough food going through can irritate the guts and make some horses footy as well as stressed grass possibly being bad. And I did have my horses on one field for a very short time that managed to give everything laminitis despite not appearing to be lush or having much on. What else is she eating, like what chaff and supplement?
Another possiblity is that she's had laminitis in the past, even quite mild can make some feet flare and get flat soled, and they've just never had an opportunity to recover since it is really difficult to get concavity back while shod. Plus once the feet have gone out of shape even really mild bits of LGL can really hold up the recovery.
Plaiting can be made worse by foot balance being out, and it being a new thing would suggest cr*p farriery and not a conformation thing. Both having problems suggests that either both are being affected by the same diet issue or the farrier needs sacking..
I used to pay £40. Most trimmers will come out and have a look at the feet and then let you decide if you want to go for it but it does help to not have a shoe in the way. A good way to do it is get a trimmer out 5 or so weeks after being shod, let them take the shoe off and have a look and if you decide not to go for it then farrier out and 'the shoe fell off'
She's not likely to be one that can have shoes off and carry on but light work in boots and pads would actually help the feet. One option is to shoe when you're competing a lot if boots aren't practical and let the feet have a break and use boots over winter or whenever she's doing less work.