How? They get endorsement deals/sponsors and they advertise those brands/merchandise to their followers. They might also sell their own merchandise (or, as one might guess, explicit goods or services). If you have good "engagement" from your fans, then theoretically you have a much greater chance of getting returns when advertising to them.
Buying a house from that probably involved decent budgeting on her part. From a brief search on her, it seems she's been doing this for a few years now.