I read your description of other mother's comments. I suggest you are overly sensitive to minor comments. Perhaps your daughter is also overly sensitive. Hopefully your daughter will learn to not take such comments seriously.
I suggest that you let your daughter deal with her own relationships. If you can, teach her ways she can respond when she's uncomfortable with the comment. Most often it's best to ignore such comments. I suggest that she answer questions that are rhetorical. She could just answer the question. I bought....
Another way is to respond with humor. Do you think I bought something sexy and pull it out to show her what she bought.
Pink stores are popular with teens. Why do you think the mother's comment was inappropriate? I suggest that either she was asking to make conversation or she was teasing your daughter. If your daughter was upset, I suggest you help her consider that there are other ways of looking at it.When you decide the mother was inappropriate, even tho you weren't there and cam't know the mothers demeanor or reason for her comment, you are teaching your daughter to take offense to comments. To make assumptions. Support would be teaching her how to handle comments. She is going to hear comments her whole life. Taking offense or getting upset will not help her get along with people or make her happy. It's very important to not take life so seriously that passing comments are upsetting.
As to the pick up situation, I don't understand why you would assume the other mother would do it. Just because it's "always" been that way doesn't mean that the other mother or you is able to do it that way all the time. You didn't make arrangements for pick up and you told the girls as you let them out of the car making it impossible for them to make arrangements. Both you and the other mother made assumptions that turned out to not be helpful. Sounds like a communication problem that can be improved now that you know she won't always be able to pick them up. You now know you need to confirm pick up. Lesson learned. Why hold on to your anger?
Anger never solves anything. Consider that life teaches us lessons, learn from them and move on.