If you don't have the ability to add apps to your company's Slack instance but still want to try Harriet out, you can create a free Slack instance by following this step by step guide.
It takes 2 minutes and it's free. But check first before you set up a new workspace - by default, any member of a Slack workspace is able to add new apps for anyone to use.
Remember, Harriet only reads your private messages with her, so you don't need to worry about her interfering with your team's work.