how great you are doing this! hmmm...having a 4 year old that is in to pin trading i think i might have to go with the little of this and that with Minnie definitely being part of it. each time we go to the park, she checks out lanyards for princesses. she has had several "favorite" princessess, as i do believe little girls go through stages of who their "favorite" is. currently it is Cinderella with her, but 2 trips ago she was wanting to find Aurora pins
not saying she'll pass up any princess pin at all, just has her current favorites. with this said, she really does like Minnie Mouse pins. if there is a Minnie pin on a lanyard, she will go for that! i say this, as i wouldn't have been able to definitely predict when we first collected who she would want to collect, if it would be what she continued to want and if the next month we'd back to the first one. we've just let her collection evolve to what she enjoys at the time. i don't remember if you said her age, but if she can understand on-line trading, i'd be happy to do so with her
this is just my $0.02 having fun is the most important.