Who says they didn't? I"ve sent an email to people before and they haven't received it and visa versa. It's email. It happens. That's why they also advise people verbally, give them their due dates, give them their reservation numbers, etc. No one can guarantee an email will be received for any number of reasons. Heck, I've sent myself an email before with a recipe or reminder and it hasn't shown up, or takes so long to get there it ends up having been worthless to send. How would Disney, you, me, or anyone else know that an email was NOT received if no one calls?
If this was hotel ABC and they did the same thing Disney did, people would be siding with the OP. There's something about Disney that gives it a teflon finish that makes it immune from criticism. Sorry it's a business like any other. The CM screwed up and didn't follow through with the email.
She would know the email was not received because she would see that it never made it to either her inbox or her spam folder.
So from here on everything will be perfect!
Have a great time!