At the very least, nearly any restaurant will have salads, and with the exception of a few salads which include lardons, most of them should be free of saturated fats, except possibly the dressing, which you can always ask to be served on the side (la sauce à part). The traditional French dressing for salads is la vinaigrette, which is oil, vinegar and a bit of mustard, though.
While there are quite a few dishes that use cream extensively, they are not predominant in French cuisine. A bigger problem (mostly in the North of France) would probably be the extensive use of butter, though not as part of the dish itself (except a few sauces), but rather while cooking (pan-frying), especially meat (and sometimes fish), so it depends to what extent she should avoid it. In southern France oil and actual grilling rather than pan-frying are more prevalent.
If just pan-frying in butter isn’t a problem, then I would expect nearly all dishes to be OK, with the exception of sauces (which in most cases can be served on the side), and the few dishes which are actually cooked in the sauce.
Not sure if fries are allowed in her diet, but if not, but even dishes usually served with thar traditionally (like the ubiquitous “steak-frites”) or on the menu can nearly always be requested with a different side (salad, rice, green beans…).
There’s a related question here. It deals essentially with an actual allergy, but many of the answers may be helpful.