All my experience is with epub rather than mobi, but the following works for me.
In MSWord, you could just create an <h2> heading 'Dedication' for the dedication section. This would give you the pagebreak you want.
If you don't want the word 'Dedication' to appear in the bodytext, just manually change the html from
<h2>Dedication</h2>
to
<h2 title="Dedication"></h2>
This would give you a 'Dedication' TOC item but the text should not be visible in the body of the mobi.