I'm sorry family doesn't understand your dd. You may need to set-up the next visit with structure for your dd. Perhaps staying at a hotel, shorter chunks of time with extended family, inviting cousins to go "with" your family places, etc.
It sounds like she needs support to help her in those difficult situations. Try to find coping strategies she can implement. If she can learn to sense when things are becoming overwhelming, she could share a code word with you. Then, you could.....xyz, whatever it is she needs to help her through it.
You probably need to work on not letting your family set you off - so difficult I know! You'll be able to handle situations much better if you are able to stay calm. It's also easier to leave quickly when you're not fighting. If you know they are against the way you parent, you can visit with your guard up. I'm sorry you have to do that. Sigh.