I haven't visited it in Orlando, but if you're talking about "Titanic: The Artifact Exhibition," my family toured it a few years ago when the exhibition (or parts of it) traveled to a nearby museum here in New York. If you have a child who's "obsessed," she will love it. It was incredibly impactful to see actual items recovered from the ship, and everything was presented in a respectful yet informative way. I'll never forget seeing a display of chafing dishes that came from one of the kitchens, nested together on their sides, exactly the way they were found on the ocean floor -- each one still with visible scorch marks on the bottom from the one time they'd been used -- possibly as vessels for the last meal some passengers would ever have! If you go, bring tissues.
We spent about 90 minutes and really took it all in (although I did have two toddlers with me, which abbreviated the visit somewhat) -- others could easily spend half as much time, or a bit more, depending on their level of interest. Do keep in mind that photographs are not permitted (at least they weren't when I went through - and it's possible it was just flash photography that was prohibited, but I no longer recall the details).