Hey there, and welcome to our little corner of the forum.
Let's see... where to start:
Mesh - Protective
Textile - More protective
Leather - MOST protective
Being a passenger (versus rider) isn't the important factor.... if you were to go down, you'd likely sustain just as bad of injuries as the pilot.
What you opt for is up to you.... down here in Florida, mesh is a NECESSITY. There's just no way it's humanly possible to wear leather year-round. Where you are? Depends.... if it doesn't get really hot/humid, you might be able to get away with a well-ventilated textile during warmer months, and certainly leather in cooler months.
Key things are this: One, make sure, whatever it's made of, that it fits YOU right. Look for women-specific gear, as it'll be shaped and cut to fit a woman's body, rather than a man's. You don't want it too loose; think about if you were to go down, and slide on the pavement -- you don't want the jacket to come riding up because it's not tight enough. (I'm not trying to scare you, I just want you to realize the importance of fit).
Also, look for CE armour. There are a few types of armour, but if it indicates it's "CE approved" it's going to give you a higher level of impact protection. CE used to be hard to find in women's gear (but was the norm in men's gear) but in the last year or so, that has changed. I believe most -- if not all -- of the Joe Rocket ladies offerings have CE armour in them, as does the new line from Power Trip. Icon, on the other hand, while very popular, and "cute," is not CE approved. In fact, if you read the tag on the inside of most any Icon jacket, there's a disclaimer that it is NOT "personal protective gear." (which is frightening, when you think that some of their men's leather jackets are upwards of $600.... )
As for helmets, many of your higher end models (Arai, Shoei, Suomy) are going to be very durable, and lightweight. Other mid-range companies are getting better, though... I've heard AWESOME things about the Scorpion Line. Check the Gear area of this site -- I've posted a huge list of "feminine" and "girly" helmets... you might find something there you like.
And let's not forget gloves. You may not think you need them, since you're only a passenger, but again, in the event of an accident, you need just as much protection as the pilot. Get some good quality mesh-and-leather or leather gloves. This will also give you a better "grip" on the tank when you're riding, and will reduce the vibrations you'll feel in your hands (which often make your hands go numb for a bit).
Hope this helps! And good luck!