Good goggles over glasses for a small head? I have a pair of prescription sunglasses that partially wrap around my face, but when I ride (mountain biking and commuting), dust and debris still end up in my eyes, and after twenty miles, my eyes are watering. I am looking to get a pair of goggles that can fit over my glasses, but I don't want to order a pair that won't fit my head (I'm 5'3"), and I have yet to find a goggle review that mentions a small size. I have a cross-country helmet, so they'd be sitting directly on my face. Are there any recommendations? I am looking to get a pair for under fifty dollars.
Safety Glasses.

I no longer bother with prescription sunglasses, I have multiple pairs of Uvex safety glasses that fit nicely over my glasses.  There are multiple lenses that filter all UV, come in different colours, etc.  I also have a pair with clear lenses that I use when it's particularly dusty or dirty.  (e.g. I sometimes ride over a very busy bridge)

If you do go with some sort of safety glasses, you can either find someplace online that sells them or look for a local safety/industrial supply company.

Here's some more Uvex-specific information, I'm sure other brands would also work:

The glasses I use are the Uvex Genesis with Espresso Lenses.  The Gold Mirror lens looks cooler (both are 100% UV) but the gold surface finish is more fragile.  The lenses on these and many other safety glasses are interchangeable so if you want another colour or need a replacement, you don't need to buy the frame.  OTOH, the frames are not expensive so it's possible to have multiple shades for different conditions.  (The last pair I bought last year was about Can$35.)

Uvex has a smaller series called the Genesis Slim that might meet your need for a smaller pair of glasses.  They don't have as many colour choices for lenses, but both of the "Grey" choices block 100% of UV.  This page has PDFs of reference info: which tints are available for which frames, details of the different lens tints.