Hmmmm...

I'm not sure if I have enough information to be useful, but I can throw a few things out. One idea is like you said, to leave a column on one side (or both) to use as a place to put the dots. Or, you could have a table within a table, and use it to have a polka-dot-filled border around the whole page.

You could also use small polka-dots in the logo, or the menu buttons. You could use polka-dots as the background image only if you convinced her to change colours, like maybe to dark grey on black, because contrasting colours in a background will me a pain to choose text colour for.

Paul