It sounds like the mom was trying to drop a hint to you that your daughter was not needed as a bridesmaid any longer. They may be reluctant to answer your texts/calls because they may be embarrassed.
As you and your daughter know, weddings are very stressful and very expensive. I'm sure they didn't intent to hurt your daughter, but they may have just realized that they can't afford the wedding they want and are simply too embarrassed to talk to both of you. Was it rude not to answer your daughter's texts/messages??? YES, but, give them a pass this time.
Just have your daughter mail a note and leave a phone message to this affect: "I recall your aunt saying that you're scaling back on the number of bridesmaids, and since you haven't confirmed that I would be in the wedding party then I'm assuming that I am not. I want you to have a special wedding day, so let me know if you need my help with anything. Wishing you all the best."
This is a great opportunity to teach your daughter to take the high road and be the better person. Not to be a doormat of course, but to be of good character and to let her cousin know there are no hard feelings. Remember, wedding planning is soooo stressful!
All the best - give your daughter a big hug!!