Please HELP! Queen after pregnancy is panting!

Zoe (the queen) gave birth starting at 6:45am on June 2nd and ended at 8:15am. She gave birth to 4 beautiful kittens. I only witnessed the first 2 being born. I assumed she was done after an hour of nothing. At 8:15 I walked in to the room to find 2 more very wet kittens. Lol About 4 hours after giving birth she started panting and having rapid breathing. I thought maybe there was another one on it's way. After 2 hours of nothing and still the same symptoms. I phoned the vet and they said to bring her in. Within 30 minutes we arrived. The vet checked her over, did an ultrasound and said he was confident in saying he didn't believe there was any kittens left and it "may" be a calcium deficiency, so to up her intake on kitten food and see if she will take whole milk. I have been giving her more kitten food, but she doesn't want the milk. In all honestly the symptoms for calcium deficiency just isn't adding up From what I have read.
I have taken her temperature and it is in the normal range. It's hot outside BUT not inside. She hasn't had any abnormal discharge from her peachy! Help! I don't know what to think! Any ideas???
I have read that panting is a signal of pain? I'm so scared for her.

So you were to the vets 2 of juni, it wasnt nothing much, perhaps a touch of calcium deficiency.  No more kittens.

  Today it is the 5ths.   So whatever it is, it is something new.   There  MAY be some aftercontractions, so you dont need to panic at once.  But if she continues to panting after you wrote the post 3 hours ago, it IS serious, and you must contact your vet again.

And make sure she gets more calcium.  Goat milk is excellent if you can get it. (better than cow milk).  Some cheese, full fat unsweetened youghurt...

Or crush some boiled egg shell into a fine powder, and give with her food... Lotsa calcium.

How are the kittens?  Does she take care well of them?

So, if she isnt better, contact your vet NOW.   @hendrixmeghan

Good luck!