My Dd also 4, has the happyland fairy treehouse and boot but rarely plays with them these days so I wouldn't personally buy anymore happyland. She's also in to playmobil and Im also considering some sylvanian families for Christmas.
It's not really Happyland though is it, it's a bit more intricate - though might need closer inspection. My 4 yr old would love it and the reduced price is quite good. Personally I think as long as there is scope for imaginative play dcs can get quite a lot of play value. out of these things for a while. I'd show her a picture of that and one if something else you think she might like and get her to pick which she likes best.
My DDs don't tend to play with happyland, and don't have the fairy house, but they are both still into fairies and might play with it if they came across one - they are nearly 8 + 6! Have said they want something to do with fairies, bit stuck for age appropriate fairy stuff.
I have bought that for my 6 year old dd for Christmas. She grew out of happyland a good few years ago but this is not really similar. I have got some playmobil fairies to go with it rather than the elc ones.