Maybe try talking to the longarm quilter first -
It's POSSIBLE she may be ignorant/unthinking/didn't realize, etc. etc.
I would also be upset with someone apparently claiming credit for doing "everything" when that isn't the case.
Are there other sites that have captions with a "pieced/appliqued by Sew and Sew" - which I think should be listed first in the caption - that you could show her as examples?
And then strongly suggest that she should do the same thing.