@expatmatt78 "she didn't offer any condolences at all" not very kind.
"didn't even reply to me"
No you are not being unreasonable, she is rude. Just tell her, she has told you before you are her only friend yet now she is stonewalling you because you could not do something with her.
It feels like she is punishing you for not being available. Ask her if she realises that you and your dh are upset and you are coping alone with the kids.
So what if other people do that a lot, single parents do it all the time! But this is not your normal and so it may be hard.
"I work with her DH who therefore has seen me in person and how I am getting on (been a bit all over the place this week)."
I personally would not assume a husband would know to report this back, Id say any spouse at all may not but some women do seem to notice this kind of thing more than some men.
"You're right I have no reason for her to know that this is a big deal." Then tell her, tell her how you are feeling and suggest a way she can be supportive to you, if she wants to. This will let you see just how much you mean to her.
"I guess I'm being unreasonable- would it be ok to say to her that I'm kind of upset then so she knows ?" YANBU and yes it would be fine to say to her this.
"Oh and also if it counts - she is also friends with my DH (the 4 of us have spent a lot of time together and gone on vacation together etc). I suppose I just found it odd for her to to reply at all when I messaged to cancel and said why- wouldn't you at least say "oh shit sorry let's reschedule "?" That is odd and suggests she is quite wrapped up in her own world.
"... because this is an unusual occurrence if that makes sense ?" It does make sense, just ignore people who cannot see that, they just cannot see it is all.
@Whatshallidonowpeople "Step father in Law? Why do you need to be checked on? You are, I'm guessing, a grown adult, look after yourself" That's really rude and insensitive. Did you mean it come across that way? People can be upset about the death of people they are not blood related to you. Grown adults can feel upset. It's not only an emotion children can feel!
extinctspecies "So she hasn't responded to one message?" It's a pretty big message. Do you think it is less important because it is a step dad. Or less imporrant because it is a FIL? If/when my FIL dies I will be devastated.
"You need to develop a bit more resilience & make it not all about you." But this situation (friend not communicating and appearing not to care) is about the OP!