Unable to add second email address to Apple Watch on family plan

Good day—

One of my kids received an Apple Watch, but we're unable to add an email account to it. She already has an iPad and iCloud account. When I first setup her watch, the iCloud email appeared on it. But she has a second email address I'd like to add. Any ideas how that can be done?

Here's what I've tried so far—

• Checked Set up an Apple Watch for a family member, but it has no information about adding an email account (and step 8 never prompted me to add one)
• Reviewed Manage mail on Apple Watch, but those instructions do not apply to watches in Family mode. In the Apple Watch app on my iPhone, which is connected to my kids' Watch, under Family Watches > Apple Watch > , there is no Mail menu at all. .And on the Watch, in Settings > Mail, there is no option to add a second email address.

Thanks for any insight!