I added someone to my family sharing. Do their photos automatically upload to my iCloud?

They don't automatically upload to your iCloud even if she is sharing your iCloud storage plan. See the following from Share iCloud+ with your family - Apple Support

When you share an iCloud+ subscription, everyone in the family group uses their own account. That way your photos, documents, and other information stay private, even though you're sharing access to the service. You simply share the features and space available in iCloud+ with your family members, so you only have one plan to manage.

To share photos with a family, see information in How to use iCloud Shared Photo Library - Apple Support