Take a sharp picture of the front of the lens with the lens cap off. It should show a thread size marking ("58mm" or some other number between 43 and 77). That's separate from the focal length description (a range for zoom objectives) that's usually followed by a slash and other numbers. Then on the top of the camera (to get a view of the flash/accessory shoe or connector available). And of course, if you have a model number somewhere, take a picture of that.

You write that she is "a very serious photographer". The problem with that is that a) she'll likely be using different lenses for the kind of photography where you really want a ring light b) she'll have pretty precise needs.

Ringlights are mostly good for product photography. When used continuously, they are not well-suited for photographing "bugs" (arthropods, usually insects and spiders) since those are sensitive to light and scurry away, so you really want something to connect with the flash mechanism. There are light guides (no active ingredients) and slave flashes to combine with built-in flashes when there is no useful flash shoe: their price point does not make them suitable for a casual gift.

In general "she is a very serious $whatever" and getting a $whatever-related equipment gift without consulting her is a recipe for relationship trouble because of her not finding the right approach for not hurting your feelings when your well-meant present does not fit within the well-carved-out needs she would use it for.

Any chance to contact any of her photographer buddies, people she works with? They could probably give more specific hints or warnings.