I'm surprised he hasn't shown it to her already with his omnitool. She's seen it before, and the only other person in the mansion who isn't a time traveler is Flandre, who has the fantastic mental flexibility of the recently-mad to help her handle it. And if he doesn't want to play directly from the tool, he could certainly use it to fabricate records for the player.

I know he seems to be viewing 1946 as sort of a "challenge run", where he doesn't use any anachronistic tech unless absolutely necessary, but surely there's some part of him who wants to fill the Scarlet Mansion with the sounds of his daughter's band rocking out.