My thirteen year old was carefree like this as well. So what I did is I gave her a certain amount and told her this was what she was allowed to spend on her clothes. I actually gave her the money in her hand. I went shopping with her and of course, I had the final say-so of the clothes she picked out, making sure it was appropriate. I let her know that money does not grow on trees and that she needs to spend her money wisely. We have big shopping trip twice a year.(summer and winter) I always give her a reasonable amount of money but she knows that she needs to shop wisely or she will not have much clothes. She learned this the hard way, of course. Our first time at trying this, she wanted to see if I would give in, so she bought with the amount of money very little of anything, but paid top dollar, and once we got home didn't care for what she had bought. I reminded her that she was given a certain amount and no more would be handed to her and that this was her choice, the money was in her hands, not mines. So that Winter, I stuck to what I said, and she dealt with it. She has now learned to shop wisely and she loves the idea of actually having the money in her hands.
The whole point is, you must set limits, stick to what you say, and make sure she realizes she is now the responsible person for how much clothes she will have or what she decides to buy. Remind her if when she gets home she does not like what she bought, keep the tags on, that way she can switch it out for something else. Don't give her additional money because then she will know she can do this all the time. And of course talk to your husband about what you want to do, so he knows exactly what's going on that way she can't go running to him for more money.
I am a mother of three. I adopted all of my children. Two of them I adopted at birth, and my oldest I adopted her when she was seven years old. She was my toughest. I had to really teach her the value of money, because she really had no concept.
Also, I have already spoke to her about when she hits fifteen. I expect her to get a job. It never hurts to teach responsibility young. I plan to open her a checking/saving account. She will put some in her checking and some in her savings each check. I really think this will help with the value of money as well. And at the same time, teach her life skills. (how to handle a checkbook,etc.) Maybe consider this.
Hope this helps! It sure made my life a lot simpler.
Sincerely,
A.