Start off with the basics. Definitely get a bullet (to me they're incredibly nonthreatening to those using toys for the first time) and bring in a traditional vibrator. If you're looking for materials, silicone is fantastic not only because it can be sterilized and is phthalates free, but because it's just a great feeling material. As far as circumference goes, 4 1/2" (to me) seems to be the perfect girth.
I don't know what your price range is but if there's one toy I can recommend to a first timer it would be the Chandra link
To me it doesn't really scream "sex toy", it has muted colors and isn't shaped like an animal or fake tongue or mouth. The packaging and all included materials have a softer feel and approach than some very crass packaged toys I've seen. It can be worn on either your finger or hers so if she's not comfortable using it just yet, you can be the one to use it first.