The image isn't linked so I couldn't get a larger image...
Women always choose aesthetics over function and you are now in a real bind.
I have a similar stand and my intent is to mount a shelf on the wall behind the tv to hold the center, but if she won't allow that then one other option might be to buy some type of monitor riser like they sell for computers and put the tv on top of it and the center channel speaker under the riser. The only issue there would be that the tv may then be too high, depending on the height of that stand.
TV
|-------------------------|
| center channel speaker |
----------------------------------------
| TV stand |
...OR you could return that stand and work with the lady to find another stand that meets her aesthetic goals but also has the required shelf for a center channel speaker.