Post-delivery panting

Our 2.5 year old Mexican mutt delivered two good-sized puppies 4 days ago.  We anticipated panting during her long labor, but we are puzzled that she continues to pant quite a lot at all times of the day.  She never did this before.  Is it normal in a post-delivery dog?  Does it pass?  Is she anxious as a new mother (she's a very good mother)?
thank you for your help.

[Aleda M Cheng, D.V.M., C.V.A]

Does she have a temperature?  Did she pass the after birth?  She may have an infection and requires antibiotics.  You really must take her to the vet.

[Bajagirl]

She gave birth in the box we prepared, but while no one was watching.  I got to her when she was cleaning off the second pup.  Her belly is soft, only milk in the teats.  Her eyes are clear, attitude attentive and normal.  We'll take her to the vet now.

[Bajagirl]

We were unable to take our dog to the vet (we live in Baja, Mexico) but we did watch her very carefully, and she is just fine.  Still occasionally pants, which we think may be because the box with her two pups is pretty warm for her.  But in every way she is normal and fine.  Thank you for your advice.