I got these cheapo ones from amazon, mainly to save my shins from the pedal pins. They've been great and actually saved my knees during a crash recently. Looks like they're currently out of stock but there are plenty of similar options on amazon.
https://www.amazon.com/gp/product/B005M16QY6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
This is what I wear every time I ride: http://www.ebay.com/itm/380697333029
And get something like this: https://www.amazon.com/Shift-Racing-Enforcer-Motocross-Motorcycle/dp/B005M16QY6
One of my buddy low sided while trying to make a 90 deg turn (Google Maps View). He is a new rider and was not too fast or anything. He probably slipped on the loose gravel that was there in the middle of the intersection.
He was wearing helmet, motorcycle jacket, knuckle protected leather gloves and jeans. So only part that got hit is his knee. Just an abrasion, nothing serious. Should recover fully in couple of weeks. Not much damage to the bike, except for the fairings (picture). I realized that he fell couple of minutes later so rode back to the intersection. Called 911 and got help from emergency services. One thing I learned is how difficult it is to pick up a fallen bike.
So guys, be wary of the damage to the knees. If you cant afford a motorcycle pants, at least get these knee/shin protectors.
Wow - sorry about your GF - I hope she recovers soon. Injuries like this one is why I am a big proponent of wearing hard shin guards under most any riding pants.