My gf just had an eye exam and got a new rx. What's the difference between the old and new rx's?

The doctor prescribed her glasses that will have thicker lenses for both eyes to correct increased nearsightedness. The old ones are fairly thick but the new ones will be even thicker.

She is more nearsighted (can see near but not far away) than she was before by quite a bit but her astigmatism is about the same. Anything 0.25 either way is pretty close. If she is a teenager this is pretty typical for the eyes to change this way. It will slow down in her late teens to early 20's (usually)

She is more nearsighted in both eyes, but her astigmatism is about the same.

This is pretty typical. Up until about age 20, nearsightedness increases. It slows down after about age 17, but it is pretty stable after 20.

She is substantially nearsighted, but you probably knew that.