I have a cousin who had an extreme anxiety attack( collapsed to ground, trouble breathing, etc etc) and her family simply watched her and did nothing. Note, they were fighting before the anxiety attack occured. Her sister attempted to call 911, but her family prevented her from doing so.

Curious, but what should i do for such a situation? Do I contact a certain group of people, seek treatment for my cousin, etc etc? This situation really creeped me out, and the internet was no use for me.

She could be having a panic attack instead. Best bet would be to get her to go to the family doctor or a psychiatrist to diagnose and treat like bralod mentioned. If she can, she should try to reduce stress in her life.

If she had a genuine anxiety attack, yeah she needs medical help.
Maybe talk to her, ask what's going on and offer to get her to a doctor, so they can figure out a diagnosis and treatment strategy. She might just need a psychologist to talk to. Obviously I don't know the situation in your family or her relationship with them, but she might have to make some changes to her life if a fight with her family sends her into an anxiety attack and they refuse to giver her medical attention.

And if, as people suggest there is a chance, she was faking, that does not mean she's not in need of help. People who really go off the rails and pretend to have a serious issue most of the time still are in need of psychological care, therapy or just plain someone to talk to, even if they don't have the exact condition they were pretending to have.

A panic attack or anxiety attack doesn't need an ambulance even if the person feels like they're dying. Their vitals are fine and their body is functioning normally they just need a psychiatrist to help them.

You need to help her. There is NO debate. Anxiety attacks are not fun and are generally associated with depression which can, if the situation is left unresolved, lead to suicide. If you don't at least 'try' to help in some way, it could end up being something that haunts you for the rest of your life.

What in the world would the Ambulance do for a panic attack? pat her on the back 40 mins later when they get their? Chances are her family reacted as they did because it's not the first time it happened nor would it be the last, you really can't expect emergency services to come to calm a person down from one of these attacks when if it is so bad that care is required her family should be aware of how to deal with the attack when it happens... not calling out an Ambulance which could be going to help someone suffering a heart attack. stroke or road accident victim.

Main issue here is her family needs to go to their GP and talk with them about how to handle a panic attack, if they haven't done so already, first step of stopping the attack.... will be stop the domestic fight going on in front of her, I mean really do you want an Ambulance to come around to their house to stop that cause? What a giant waste of emergency services time.... well at least the wrong emergency service if there is an actual fight happening.

Yea, it isn't the first time.

Yea, I figured the ambulance was the wrong choice. 

It just sucks when you realize people can be this cruel.

Well it's very likely that her family have encountered her having these panic attacks before in the past, both real and possible fake ones brought on just to draw attention to her to try to stop family from arguing and stuff. I'm not saying that was the case when you experienced it, but family knows family best, Don't think of it as being cruel really just.... more aware of her condition or more experienced in it than an outside visitor to their home.

Like I said though, it's very likely the family have gone and talked with at least a GP about what to do when these attacks occur and how to help her with them, I'm sure if they got to a point where she required help they would be versed in how to apply it.

You shouldn't do anything.
It's not your family so you shouldn't get too much involved.