Oh yeah!!! Very possible!! We experienced this a few months back. We had brought in the three feral kittens and knew they needed to be fixed. We just weren't able to fit it into the work schedules but thought we had a little time since they were only about 5 to 6 months old. The little girl showed NO signs of heat but got really fat really quick! I kept it to myself because I thought surely NOT! Then during a belly rubbing session I felt the kittens move! I had to fess up to the hubby then that we had waited to long. I wish I had a picture of his face since he had said that there was no way we were having any more cats. (that was about 5 cats back!!!) Anyway, to make a long story short...it was too late to do anything about it so I decided to just be excited about new babies! Because she was so young and tiny things did not go well at all! She developed an infection (unknown to us) but managed to deliver 1 live kitten while we were at work. The second, and third kitten I had to help deliver, clean, and cut the cord! One was still born so now we had two alive but she was in trouble. I called the vet several times and he kept reassuring me but said that if I really thought she was in trouble to bring her in. I thought I was being over-protective and paranoid so I left her alone utill the next morning. She was still trying to deliver another kitten. I called the vet again and he told me to pull it out. I had to do it right then! YUK! It too was still born. As the morning went on I noticed she was going down pretty quickly instead of feeling better. I grabbed her and the kittens and headed to the vet. She had a 105 degree fever, two undelivered kittens inside of her and she was dying! I have never felt SO GUILTY in my life. I stood in the office and bawled like a baby! He said he would do everything he could to save her. He had to get the fever down before he could operate and didn't know if she could make it that long. He called us late that night and said that he had had to operate and she was touch and go but still alive. He said her uterus was full of pus (sorry) so he had spayed her while he was in there. I was glad to hear that but he said that when doing a c-section they don't want to spay them because it is incredibly dangerous. She had so many things against her and I had two tiny babies that had never had a drop of mothers milk. She was dry due to the fever. I managed to keep one of the babies for two days and the second one for four days before they died. It was horrible!! On the third day the vet called and said Pervy had made a remarkable recovery and he thought it best for her to continue healing at home. Thank God today she is a fat, and sassy little girl. I don't think I could have lived with the guilt if I had lost her too. Sorry that this is so long but this happened shortly before I came to PT and I have never been able to tell the story to cat lovers who will understand the trauma for me, my husband, and most of all little Pervy.
the moral of the story...YES she can be in heat and it can lead to trouble when they are so young. Good luck and I recommend a vet visit soon!