Angela, these types of joints often can be acheived, but finding the correct angle resolution can cause a brain cramp when attempting them without the right tools.
One way to find the correct angle is to hold a piece of crown in place on the kitchen ceiling, with it extending past the ceiling change. Draw a line on the wall extending past the start of the vault a few inches and on the ceiling until the vault begins. Now place a section of crown on the vaulted angle which extends just beyond the horizontal pencil line on the wall. Mark the crown where it intersects the 2 lines, and using a small square connect the 2 points across the face of the crown. Place this crown in the miter saw and adjust the angle of the blade to match the line. This is the angle which needs to be used for the vaulted side of the joint, with the kitchen side being the same angle in reverse. It's a good idea to test the angles with scraps first to make any fine adjustment needed.
Other options might be to use a decorative block at the juncture to terminate the horizontal crown & begin the angled, or to not connect the two & return each to the wall separately, staying away from the juncture 6" or so. Hope this helps you!