We have some sort of Calico Critters (or similar thing...) grocery store that I bought for $20 at Target ($60 on Amazon...?!?). It's an old-fashioned type general store, and it came with honestly about 75 tiny little pieces...jars of candy, lollipops, bottles, real little brown cloth sacks, loaves of bread, and on and on and on. We have one set of animals for it...a family of owls.
My seven year old is the one that wanted it...but you know what? She doesn't play with it. However, my two year old thinks it's great...but then I imagine that's because she loves to dump all the pieces on the ground. She does, however, manage to grasp a tiny broom in one hand and a tiny dustpan in the other and say "Mommy, I keening!" which is adorable. :)
Long story short, I think the best age is somewhere between 2 and 7...so that might be the perfect age for it.
My oldest never really dug her dollhouse, either...and she has a super nice one with all kinds of realistic mahogany looking furniture and accessories (I mean, the thing even has a baby grand piano and a stainless steel toaster that pops up little tiny pieces of toast that you can put on tiny little plates! And on and on and on...a wooden drop side crib, a brass coat rack, and everything else you'd think a little girl would want.) I think it's just her, because I would LOVE TO PLAY with that dollhouse...and I always played with mine when I was 4-8.
Calico Critter houses are extremely expensive (I think?), and then there's all the accessories, etc...but a dollhouse can be very expensive with all the furniture, too. I think a better idea would be to pick one or the other...you know her, what do you think she would like more? I think either is appropriate for her age.
Sorry for rambling, that must just be my mood tonight. :)