No, she is not dead....
...just the subject of a likely fake "internet death hoax."
I was alerted to the death of Judi Dench in a Facebook ad that offered a full report. I didn't click through, but went to Google and searched, and also looked in IMDb news reports. The Google search yielded a single relevant hit on the domain mediamass.net, which led to a page claiming Judi Dench was the victim of an internet death hoax. Searches in Facebook and Twitter yielded *no* posts relating to the death of Judi Dench.
I suspect the ad I saw would have linked through to this fake report. It's just click bait. Stay away.