Boy, I remember when I was in my first tri-mester and hadn't told anyone I was pregnant, and then came to work the day after Open House night. . . I should not have been in work that day.
I remember the time I got the chicken pox from the kids down the hallway at the apartment I lived in, but didn't figure it out until about 20 minutes before school started, and got sent home. I had subbed for a fellow teacher during my prep the previous day, and one of the HS seniors in the class was pregnant, so she had been exposed, and needed to go to her doc as a result. Oh, and the chicken pox vaccine came out one month later.
Or the time my doc missed that I had an ear infection, and I got delirious as my fever shot up, and I got so weak that I missed two weeks of school straight.
Or the first time I subbed for K, and I got sick two days later because new teachers typically do not have strong immunity to the germs that that kids bring to school. We always have a lot of kids absent in September as they start spreading germs around at Back-to-School time, and we always have new teachers getting frequent colds.
I remember sitting in my non-air-conditioned classroom on the third floor of a very old school building with one small window on a 100+ degree day with a dizzy spell due to the heat that should have sent me home, but there is no way I could have driven home, so I stayed in my classroom.
Or the year my grandmother, my husband's mother, my husband's aunt and my grandmother's sister died two months apart.
And I think of the times I have done all-nighters to finish grading or to make a special assignment that I knew the kids would enjoy.
I think of the Sundays my husband takes my daughter somewhere family-oriented and fun without me while I check papers.
I think of the money I have spend on books for my classroom library.
I think of the times I arrive at 7 a.m. and leave at 7 p.m. or later.
My co-worker didn't want to be gone today, but she had a medical procedure that couldn't get scheduled over the summer. Then she attended her child's IEP when she should have been in bed, but she waited the three hours for the meeting before she got to lie down as suggested by her doctor.
Very few people in the teaching profession are mindlessly taking days off. She's probably more upset about missing work than you are worried about her missing work.
Being out of the classroom is fairly stressful. It takes longer to prepare to be gone than to just go in while feeling unwell.
Every teacher knows how important it is to be in the classroom in the first months of class and would rather "die" than do it. I bet she has had no other options.
I like the prepare a meal for her idea.
You could also ask if she could use some help during the class and offer to help the kids with their reading or writing.