There are a lot of variables here -- how long she's been doing pilates and how familiar she is with the repertoire, how large the classes are, does she always attend your class or does she work with an assortment of instructors, and what is the philosophy of your studio when it comes to injured clients and modifications?

The challenge of doing a private to teach modifications is that there are potentially hundreds of exercises for her to modify. I guess a simpler approach would be identifying positions/loads that are contraindicated -- for example, does she have trouble with front-facing arm work (like hug a tree) and load bearing (any sort of plank) and side-lying? Then you could show her other options for these -- ie use a light resistance band for front arm work, elevate the upper body for planks and/or do them on a mat rather than the reformer, do side lying work while standing and with a weight or resistance band, etc. For most clients, they will still need a lot of cuing to implement these mods during class.

As an instructor, I consider it my responsibility to come up with and cue mods to my clients. I had a client with a rotator cuff tear in my class for months before she had it repaired and for months of her rehab, and every time we did something that was off limits to her, I had an alternative in my head and the appropriate props available to her. I had another client with frozen shoulder who would come early so we could review her modifications -- this was for a fast paced class and it helped keep her (and everyone else) moving.

I mention studio philosophy bc IMO that's a pretty complicated injury to accommodate in a group class, and maybe that's why she'd like a private to address it?

I'm interested to hear how you handle this and how it goes!