A mother / daughter relationship can often be tested when Prom comes around. This article will help you survive shopping for the dress.
If you are fortunate enough that your daughter wants you to go shopping with her, take her up on it. You will have more input if you are there at time of purchase. Plan a day that will work for both of you and get an idea of what stores she'd like to shop at. Now comes the hard part. If you are on a budget you need to let your daughter know ahead of time. Make it very clear how much money you have to spend on not only the dress, but shoes and accessories too. If you think your daughter may try to weasel more money out of you when you are actually in the store, you may want to consider this idea. You can give her the money in cash before going shopping and tell her when it runs out she doesn't get anymore from you. This will give her the responsibility of keeping track of the money. She will feel like you trust her and treating her more like an adult (obviously not a full adult, otherwise she'd be paying for it all herself). If you do this, don't nag her about what things cost while shopping. You have given her that responsibility so let it go and she'll have to live with the consequences. When planning your shopping day, suggest buying the dress first, that way the worst consequences she'll suffer if she doesn't watch her money is having wear shoes and jewelry from home. But don't mention the second part to her or she'll feel like you are patronizing her.
Sometimes body image issues come up when shopping for a prom dress. It doesn't matter what size or shape your daughter is, all girls have something they don't like about themselves physically. When she brings it up (and she is likely to) go ahead and do the mom encouragement thing, "No you look fine" but be very careful to not make her feel stupid about her being insecure. If you do that she will never confide in you again. If you see a dress that really isn't flattering on her it's fine to be like "That one doesn't look as good on you as this one does," but always make it about the dress, not her. Remind her that it's about finding the right dress for her, not her having the right body for the dress. Also, when she is trying on dresses encourage her to pick out something she will be comfortable wearing all night. She can look beautiful and be comfortable at the same time.
Now that you have survived the dress shopping, get ready for the rest of it. Prom isn't over yet. But be sure to take lots of pictures of your daughter leaving for prom in her beautiful dress. Hopefully you will be able to look back at the whole experience fondly.
