I don't think there's an actual link between the exchange rate and her crossdressing claim. I think she just blurted out the first thing she could think of that was less embarrassing for a toddler than obsessing about exchange rates.
I think I don't know what I'm talking about.
*swallow*Um... Tatsuya-kyun is...Uh... He's a cross-dresser!!I thought that would be the case...Imagining a Madoka with a penis, it could work...Madoka!!What's that you're drawing?...closing prices!?
The kanji "円", most commonly read as "yen", can also be read "Madoka".