All vitals are fine ? No asthma
My anxiety attacks feel like breathing issues, pain and tightness of the chest, feelings of dread, like I’m going to die. It’s crazy. (In saying that it very well may NOT be what’s happening - could deff be medical and needs to be checked)
It sounds like anxiety/ panic attacks. I would definitely keep the cardiologist appointment just incase. I have severe anxiety, and when I get bad panic attacks my legs and arms go numb, I feel like I’m walking with noodle legs. My chest feels like I have a device around it squeezing the life out of me and my breathing is really fast and shallow. The first time I had one I thought I was legit dying and called someone over to get my newborn baby. I was so scared.
Did they do an EKG? If not they should of.
Also as long as her blood oxygen levels are 95 or above (can be checked with an oximeter) her lungs and oxygen intake is totally normal. Her pulse during these times can be high- from anxiety as well.
I use breathing exercises to help calm me, I go outside for fresh air and listen to calming anxiety meditations- lots of apps for those things- kids too! My children also have anxiety, not as bad as mine, but they do have it on some level. Good luck! I hope things get better! 
Sounds like a panic attack to me
That sounds like panic attacks. They are terrifying and when they hit, you lose all rational thought and are convinced you are dying. Bless her 
So I’m going to be different here with my answer for other than anxiety and that’s only because of my experience. I was having episodes of chest pain kept going to get it checked and fast forward 5 years later, I was checked for a genetic disorder and it came back positive and no one in my family knew about it. I had other symptoms that showed on Holter monitors and then MRIs. The point is, don’t stop getting answers. Make sure everything is fine. Have the tests done if you feel something is off. I didn’t. Since finding out I’ve has multiple heart attacks and will eventually need a heart transplant because of the type of rare condition I have is very progressive. The doctors and nurses thought I was having an anxiety attack the first time until lab tests showed I was actually having a heart attack. You should have seen the looks on their faces!
Now it could be anxiety and that shouldn’t be ignored either. Get her into therapy while ruling out cardiac.
This will sound funny but during those episodes… tell her to bear down. Like having a bowl movement or childbirth. It’s called the vasalva maneuver
Mayb shes having an anxiety attack nd they feel like they r going to die they breath out very fast she must try breathing in a brown bag or deep breaths by a window or outside close her eyes to calm own
Try another ER if you have one. If she is asking- do it.
It sounds like panic attacks. Feels like all those symptoms
Chest pain can also be caused by acid reflux. It can literally feel like you are having a heart attack with severe pain which then makes you anxious and causes you to panic and then not breath. I agree with others get her a pulse oximeter. If she is getting enough oxygen during these episodes that she has chest pain it’s probably acid reflux. Try over the counter Prevacid or pepcid until you can get to a doctor to have it checked because they can prescribe better medication and make sure she does not have an ulcer.
She need a therapist preferably psychiatrist sounds like anxiety