Diane
The basic steps.
1. I drew out a vertical and horizontal guide to define the lower right portion of the frame. Just a visual reference. Not a real necessity.
2. On a new Layer with the marquee tool, draw your frame.
3. Because you have a transparent selection on a transparent layer, you must use the Edit->Stroke (from the
PS menus) to stroke your frame. Make sure you have INSIDE button checked as the source of the frame placement. (Center or Outside will give you rounded corners and the pixels may fall outside your desired frame)
4. On your background layer, create a loose selection around the areas that you want to "pop" out of the frame. I say loose, because the only part of the selection that needs to be accurate is where the frame and petal edges meet.
5. Jump your selection to a new layer (Command+J on a Mac). Or use the menu option Layer->New Via Copy.
6. Change the stacking order in your layers palette so that the petal selection is on the top.
ADDENDUM....
At step #4 you may alternately just add a reveal all mask (White) to the frame layer and use a 100% opacity black brush to paint away the frame area that overlaps the petals.