I am wondering exactly why YOU don't finish it. Is it because you simply don't have the time? Is it because you don't have the interest? Or is it because you don't have the knowledge? At least two, and maybe all three, of these reasons could be remedied.
Not having the time is the toughest one of the three. But I think if this is the case, maybe your priorities need to be re-examined. Does your everyday life/work get in the way? If it does, then you need to slow down. MAKE the time to build the dollhouse for your daughter. She's 13 now. Time flies, and sooner than you like, she will be out of the house and on her own. Wouldn't it be great if she could take something that dad built for her, and pass it on to her daughter, rather than have her take something that dad bought for her? Reminds me of Harry Chapin's 1974 song "Cat's in the Cradle". If you haven't heard it, Google it and listen to it.
If you don't have the interest, then maybe it's because you are doing this project on your own, with no one to appreciate what it takes to build something like this. Is your daughter involved in helping you build it? Does she even have an interest in it? If she's not helping, ask her to. Ask her how she would like this to look and how she would like that to work. Ask her if she could help you with it because "you are having trouble deciding how this should be done". Get her excited about it, and I'll bet when you see her making decisions and offering suggestions, you'll get the fever to make it like she wants it.
The easiest one to fix is not having the knowledge. Read books on building, decorating, electrifying, etc. the dollhouse. Research the internet and see what others are doing with their dollhouses, and what is available for them. Check your local hobby shops and craft stores to see if there are any "dollhouse building clinics" available. If all else fails, just jump in and start working on it. When you make a mistake (and you will), fix it, take it as a learning experience and move on. That's how 90% of us learned to do what we do in woodworking. Remember. It's just a piece of wood. It can be sanded, shaped and/or replaced if it gets screwed up.
Above all, have fun with it and enjoy the time with your daughter while you can. I'm sure the dollhouse will mean much more to her if it was built by dad, or it was built by dad and me, "back when I was a little girl".
I don't mean to go off on a parenting rant, so please forgive me if it sounds that way. I have no intentions of doing that.
Don't ask me how I know about these things. Let's just say I do because I have a 27 year old daughter and a 23 year old son.