What we like is an extremely personal choice.... I'm the same as your daughter, I avoid too much black purely because I have four black and white dogs (who only shed their white hairs of course) and two creamy coloured cats. So I prefer the white background.
But... keeping in mind these are for the swap, I think either would do just fine, honestly! :-)
Learning to pick what YOU like, and ignoring the rest of the world, takes time. ;-) Don't be too hard on yourself.