You're correct that she must be registered with DU first. There are three different types of contests:
1. Monthly
2. Seasonal
3. Calendar
For the monthly contests, the winner of the most recent contest is responsible for running the next monthly contest. The first thing that happens it the selection of the theme. Some hosts will choose the theme on their own while others get suggestions and use polls. After the theme is announced, a submission thread for entries will be created. Here's the submission thread for the currently running contest:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=280&topic_id=74701&mesg_id=74701The rules are written in the post for submissions. (Generally speaking, longest side 800 pixels, file size < 200K, host may not enter. Read the rules in the thread for much more detailed rules.)
If you have a photo to enter, post it on an image site (photobucket, flickr, etc.). Reply to the submission thread with the subject line as the title of your photo and the message as the link to the photo. Do not include any other info (any comments you make can be done in the comment thread).
The seasonal contests are similar to the monthly contests with a couple changes. The theme is not random - they'll be something like "scenes of summer". There are two hosts so the host can enter (abdicating responsibilities to the other host if their entry makes it to the final round). Other than that, it's pretty much just like the monthly contests.
The calendar contest has much different rules than the other two, as there are more winning photos and they need to be high enough quality to be printed. Here's a link to last year's calendar submission thread:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=280&topic_id=54131&mesg_id=54131We're close to the projected schedule for the calendar (theme is Architecture) so the submission thread should be soon. The current monthly contest is in the voting stage so it'll be about 2-3 weeks before submissions for the next monthly contest. The last seasonal contest was in May so the summer one should be early August.
I look forward to seeing her photos.