If you look around, the HW45 is frequently for sale with both .177 and .22 barrels. Then you can say "it's different", .22, and "oh look, it's come with a spare barrel in case I wear one out"
Best of both worlds.

And if you really need an excuse to buy more pistols, show her the UBC competition results site. There are four categories for four different types of pistol, and you'd really really like to be able to compete in all four.