I'm helping my student w/ her dissertation, and she wanted to include slides for all 3 chapters in 1 pdf (using beamer).

We were working on this, but when we created "outline for the presentation" for each chapter using the table of contents, there were sections from other chapters that showed up, which we didn't want to show yet. We originally thought about using \section* command, but then that section didn't pop up in the other outline for the other chapters.

Is there anyway to show table of contents for specific sections only (i.e. sections 1 thru 6 and ignore 7 thru 18)?

Use \tableofcontents[sections={<list of section ranges>}]:

\documentclass{beamer}
\setbeamertemplate{section in toc}[sections numbered]

% helper
\newcommand\oneSecOneFrame{%
\section{Title}%
\begin{frame} contents \end{frame}}

\begin{document}
\begin{frame}
\tableofcontents[sections={1-3}]
\end{frame}

\oneSecOneFrame
\oneSecOneFrame
\oneSecOneFrame

\begin{frame}
\tableofcontents[sections={4-}]
\end{frame}
\oneSecOneFrame
\oneSecOneFrame
\oneSecOneFrame
\end{document}