One of my students (I'm a balletteacher) wants to be able to do this:

She is pretty flexible in her back, something like this,

but I don't know how to help her further.

Can anyone help me with a good build up program to help her to reach her goal?

Cool! Welcome to the rhythmic stretching world!

Start with cobras. When she reaches about 90º degrees, it will be hard for her to support herself with her arms, because she will need to stretch further. So, you come in!

When she is feeling little stretch in the cobra, (say after, I don't know, a week?), get her to lie on her stomach with her arms stretched out (next to her ears), and you will sort of sit(?) on her ankles without putting much weight on her, only enough to hold her ankles down. Then grab her hands/wrists and support her elbows and pull her backwards, like in the photo above, except you are holding her arms, not the metal. Hold for 10-15 secs. And do NOT push this stretch.

Sorry for the detailed explanation! Hehe

Sometimes while doing that stretch above, let her bend her knees near her head.

When her feet are close (say, 3"?) let her try the cheststand.

Check the Stretching stickies also, and read the Advanced back stretches.

Thank you for your help! I didn't think of doing it this way. I checked the Stretching Stickies, but couldn't find what I was looking for (didn't look well enough?).
We will work on this and I'm exited about how the results will be.

www.dance.net . . .

Here it is! Sorry, my mistake, it was under the 'Links to Good Posts' section.

Oh, and also, in this post, they mention a headseat. I wouldn't personally recommend this move. I think it's dangerous because you have the possibility of falling on your head if your balance isn't right.