On the flip side I have many friends who teach in private schools. They do no email weekly themselves. Sound like your SIL went from one extreme to another and struck it lucky with this teacher.
I'd hate for you to think public teachers don't care. I'm extremely passionate about my job and care tremendously for the children in my class. I've spent many many nights stressing and devising actions to take as I'm worried about a child in my class and I put hours into prep and spend a lot of my own money on these children. I'd hate to think that because I didn't send a weekly email it meant I didn't care.
Hopefully your SIL isn't disappointed if next year with a new teacher the emails stop.