Hello, my name is***** and I have over 20 years of experience as a veterinarian. My apologies that this question wasn't answered promptly because this is a true emergency situation. I am sorry to hear that this little one is making a squeaky noise when breathing today and her abdomen is moving up and down rapidly. That sort of motion is called abdominal breathing and signifies great difficulty exchanging oxygen.
A normal bunny has a resting respiratory rate of about 30 to 60 breaths per minute depending upon their activity and stress level, and one breath is considered the in and out motion of his chest. If she has a rate faster then 60 breaths per minute then she is in trouble.
If you can notice that she is breathing abnormally then I am concerned for her. Bunnies are prey species, which means that they do all they can to hide an illness until they are so sick they simply cannot. That means a noticeably sick bunny is often much sikcer than it would appear.
If she doesn't have a nasal discharge and isn't sneezing then her difficulty breathing is likely related to a problem in her chest or secondary to anemia (decreased numbers of red blood cells).
Problems in her chest leading to an increased respiratory include primary heart disease (including cardiomyopathy), lung disease including asthma, bacterial, viral, parasitic (lungworm) or fungal infections, a mass(es) in the chest including lymphoma, heart based tumors or carcinomas, or fluid around the lungs (pleural effusion) due to a mass, bleeding, chylothorax or an infection.
Anemia can be secondary to poor red blood cell production, either due to kidney disease as the kidneys make a hormone to stimulate production or primary bone marrow disease, or anemia can be due to bleeding or destruction of red cells due to a tumor, blood parasite or autoimmune disease (body attacks its own red blood cells and destroys them).
If this girl's tongue and gum color are a nice bubblegum pink them she is in better shape then if her gum and tongue color is blue or gray, these would signify she is in dire trouble. This is a true emergency, and it best that you seek veterinary care for her now.
The conditions I listed above are serious and I would highly recommend that your girl see a veterinarian promptly to have an examination and further testing done based upon her examination. She likely needs radiographs of her chest to evaluate her heart and lungs to start and then further diagnostics based upon those findings.
In the meantime keep her quiet so she can breathe as easily as possible.
Please let me know if you have any further questions.