The name Walmart is copyrighted, but that doesn't mean
The name Walmart is copyrighted, but that doesn't mean I can't refer to it in a web post. Similarly, "Gioavonni's Bridal Boutique" may be copyrighted but that doesn't mean I can't post the name on the Internet. (In fact I just did.) Your attorney relative could send a letter to her claiming that she is violating copyright law. This would be a lie, but it is commonly done in the business world.
Furthermore if she thinks the dress is "frumpy" and that it's your fault, that's her subjective impression, and she has a right to her subjective impression. Unfortunately, you can't sue her for that. If she says things that are clearly untrue, you can sue her for that.
I am sorry to hear that you are being unfairly attacked, but you haven't provided me with any evidence of anything she has done that you can sue her for. She may have said things that you could sue her for, but what you have mentioned so far does not sound like things you can sue her for.
