I agree. Why even mention that you plan to? They will put offers to rebook on your bed at night. Just tell her you can't afford it right now.
If she does come on the cruise, find a moment alone and swing by the future cruise desk on deck 4. Even if it's closed you can fill out a post card and drop it in the box. Even if you're not sure what exact date you want, just book something. If you want your same TA to handle the new cruise, put that on the card too. You can tweek it later. It would take less than 10 mins to fill out the card. They can put the deposit on the same cc connected to your onboard acct.
Then zip it! You will be excited but as tempting as it may be to share your excitement, don't even mention it to your kids.
You will hopefully get a chance for a do-over. Unless you live together, I wouldn't even mention when you're gone. List a good friend as an emergency contact.
I'm glad my parents are easy to cruise with. (and I'm not just saying so because my mom reads the Disboards!)
We've always been in agreement that we have different likes/dislikes/abilities/disabilities, etc and sometimes we need to each do our own thing. On our Alaska cruise, I think we only spent dinners together & our horse-trolley ride in Victoria.
We've probably done around 10 together. I hope your kids find some happy memories with their grandmom.
I would definitely be carrying on my own alcohol & earplugs.