What about doing simpler like taking the beautiful, original Dragon's Lair sideart file from vectorlib.free.fr and changing "Dragon's Lair" to " _____'s Arcade" using an similar font?
From my experience with photomosiac software, it sounds like it would be pretty easy to run a quick demo of what it would look like for your daughter and see if she likes it. In the end, you have to make her happy, right?
Also (and someone please correct me if I'm wrong), most large-format printers that will make sideart for you will probably print at 120dpi. I'd make sure in Photoshop that the little screenshots are legible (reformat the sideart to actual size + 120 dpi).