I'd say chill out. Be happy your significant other shares your interests and remember that most people start this hobby with a fish very similar to the ones she has chosen.
everybody has to start somewhere and i started with a 30 cube let her enjoy what she has now and if she really likes it. show her the enjoyment of feeding time with south american chiclids my fish of choice.
Chill out man. My girl has been keeping fish longer then me, and she has a 10 gallon live bearer community. When I get a bigger tank, she wants my 55 for a larger livebearer community.