It's that old steer them towards the direction you want and let them think it was their idea or they had equal input and then agree.
That is from the book, How to win friends and influence people.
I must admit, mine has always made more money then I do and not spent it. She would agonize over something she wanted(New camera) and I would just laugh and insist she just get it. And she knew I am a Tim the Tool Man type so the things I did were satisfying my need to "make it work". Plus most of the time I didnt blow up the house and it worked and saved us money.
Keep working on her, it is to good to be true.