Anonymous employee feedback tools are crucial these days, and Google Docs will not be the solution. Here's why:
1. The link that you share with your team is open. So if someone forwards that form to someone outside your company, then you have no clue who the feedback came from. It could be your ex-employee too.
2. You need to spend time framing the questions, and you need to put in a ton of effort in thinking through the entire process.
Instead, try a tool like
https://understandbetter.co/ which has customers like Chargebee, Spritle and many such companies. And they use the tool to provide anonymous feedback in a jiffy.