Your girlfriend may feel that the womens black dress shoes that you purchased for her are too tight and she won't be able to wear them. Just so you won't feel bad hopefully she has let you know that she really loves them and would like to get some more but you accidentally bought her the wrong size.
Every girl knows that when you wear shoes on your feet that hurt, you will not only be in pain but you will also have blisters. Once the skin starts peeling off of them, then that's when it would hurt worse. Hopefully you will understand what she is trying to explain to you and see if you can get her another size.
It's off to the store again to see if you can try to exchange them but this time make sure you bring your girlfriend and she would need to do all the talking to the sales rep and see if she can exchange them for another pair in her size. Some stores won't let you exchange anything without a receipt but all she would have to do would be to let them know that she has received those as a gift.
You don't want her to tell them that you got them for her because the salesperson may ask for a receipt from you when you don't have one. If you feel it's best, rehearse what you're going to say in the car so she would know not to mention you at all. The only reason why you're there is because she wanted you to come.
In the worst case, the store clerk may recognize you as the person that bought those for her and she may automatically ask you for a receipt. If you don't have one, then she may not let you get another size for free. To avoid this situation, recognize what store you went into before going in there. If you have been in there, she wait outside and let your girlfriend do all the talking.
That may be the only worst case that you may run into and you may not have to worry about waiting outside and are able to go in with her and watch her try them on. The exchange was successful and your girlfriend now has a brand new pair of dress shoes that are her size. When the two of you go out together, she will have something comfortable to wear on her feet.
To avoid having to return womens black dress shoes from your girlfriend try hinting around to see what size shoe she wears and then you won't have a problem. If you find that to be unsuccessful because she might think of it has being suspicious, then ask one of her friends that knows her best and ask her what shoe size she wears.