Yes, I know I'm not a bad mom. It was just the hindsight talking. I was wishing that I'd thought to suspect strep, and I was worried that K would catch it because I didn't treat it nearly as soon as I should have. Thank you, everyone, for your comments!
We saw the doctor this morning, and thankfully she does not have strep. She does, however, have sounds in her left lung that the doctor characterized as possible "walking pneumonia". I'm not frantic at all about that, and I suspected it because I kept hearing "rasping" noises as she breathed in and out. I'm SO glad I had it checked out. Turns out amoxicillin won't touch walking pneumonia, but Azithromax does, and I'm happy that I only have to give it to her once a day for five days. Hopefully we'll both be on the mend soon!