Thanks. I want to see you have great success,so I took a few minutes to pull the EXIF info and make a post so you and everybody could see the technical information like focal length and f/stop and evaluate the degree of foreground and background depth of field each lens choice brings with it.
What makes outdoor fill-flash so tough with the 20D is that you are limited to 1/200 second and ISO 100 and smaller f/stops,and you live in San Diego! You can move into shaded areas, either heavy shade, or open shade, but you STILL MUST maintain the 1/200 shutter speed and a smallish f/stop to keep the brighter,background areas looking relatively normal.
YES, you are right; you know her, she's your S-O, so you feel odd photographing from a distance. This is a zoom lens problem. If you had to shoot with a Canon 135mm f/2 L or a 100mm f/2 or a straight, non-zoom lens of even 85mm, you would *never* be as close as 21mm gets you. Just as an aside, the 135mm f/2 L will give absolutely dreamy,delicious transitional rendering between the in-focus and the out-of-focus areas on a 20D...it gives an almost ethereal rendition to everyday scenes.
Because of the light level (So-Cal), 1/200 second top flash speed, and ISO 100, you are forced to use small f/stops...to counteract that, you need to use a LONG focal length lens to avoid getting really deep DOF, unless you really,absolutely need to have deep,sharp focus, like to sell a product or illustrate something. It might seem weird to be 40 feet away,but it works pretty well.
Instead of fill-flash, you could use reflector fill lighting. A 42x78 inch,horizontal reflector made out of PVC pipe and fitted with a silvered, metallized fabric, or a white,reflective fabric would help you literally "see" what your fill light was doing,and would give you a bit more exposure flexibility. You can make these out of $12 worth of Home Depot white PVC pipe, four elbows, and a hacksaw in about 15 minutes. With an assistant holding a large reflector like that, you can fill-in shadows and get away from flash, and gain back the wider lens apertures that the sunlight and 1/200 steals from you in So-Cal sunlight or even shade.
Best of luck to you. You'll learn very fast if you keep this up for long.