To me, she is asking for a super shiny finish to the floor. That could be the only thing I can think of.
This may just require more than one coat of finish. If I’m not mistaken, travertine is like a stone or is a stone and will drink up the solution so pack em on buddy.
I’m not sure what a travertine floor is but I have had several customers ask for a shiny finish on a ceramic floor and I have just flat refused to do this since it was not a recommended practice by the tile manufacturer/distributor.
Your customer wants her stone to be polished. This is achieved with a special weighted floor machine (not the nobles buffer) and polishing powders or metal/resin diamonds (if there is lipage). I recommend that if you want to get into doing this type of work take some courses as the liability is steep. Then set up a test floor in your garage or somewhere to practice on. The money is great as you can make in the range of $3-$8 a square foot.