My suggestion is to hit up the Social Security Administration website: https://www.ssa.gov/oact/babynames/. Go back a century (or to some era of choice), walk the list, find one that you like that isn't even in the top X these days and you'll be fairly safe. You'll end up with a reasonable, not-ridiculously-unique name that this generation mostly doesn't have (the site has recent years and names don't usually go from unlisted to popular overnight).

> the popular girl's name of the decade, apparently.

Keep in mind, in the internet era it can actually be nice to have a bad-SEO common name (though that's often dependent upon surname too).