Annabelle should be cut to the ground when it is dormant. If it is cut too late it may not flower. If it is not pruned it tends to fall over. I would still prune it now. The worst that can happen is it will not bloom, but you will still have a nice looking plant.

I'm including a link for all different hydrangeas. This website is something else. It'll tell you all about the Annabelle, among the other types too. The link is for Annabelle, but you can click on the different links if you want to check out the others. Just scroll down to the pruning link. I've got a Pee Gee and Endless Summer. I'm really happy with both.
Good luck with yours and enjoy!

Kat

Here is a link that might be useful: Hydrangeas - Annabelle

Cut it to the ground and don't worry about it not blooming. Those things are like weeds.

Dave
Franklin