TisMe I don't think it's resentment that life is as she has it, I feel it's more resentment that that she has this lifestyle, provided by DH. In his mind the one time her being a SAHP is beneficial, he's being asked to change his work arrangements, so she can attend what is essentially a hobby.
If you think about it, DH has a high paid job which in it's nature incurs a lot of stress. So for DW to say oh DS is ill, I have my hobby on a Thursday, can you shift your job about, he's going to go, hang on a minute, my salary pays for all these extras that allow you a pretty decent life, the one time you being a SAHP has benefits, i.e. You're there to look after DC who is ill. You want me to change all my plans, just so you can study a hobby. Are you being serious?
I think if you look at it from his angle, you would be
as in your mind, throughout the time DW has been a SAHP, OK when he was younger it was more challenging. But in all reality he's been sick a few times, looks like a bug of sorts, surely he can be left alone a short while whilst you go off and do whatever.
Even if she had to do cleaning, dog walking, laundry, any working parent would surely say, I work my arse off so you don't have too. Are you being serious you want me to be there just in case.
As per the title AIBU to 'expect' DH to work from home. Not AIBU to suggest or ask. OP pretty much has it in her head that the course is more important than DH's work.