On Twitch (and Youtube now) the people who watch the stream can donate money during the stream.
Youtube has a system where you can pay to have your comment at the top of a chat box during a live stream, and that money goes to the creator. I was watching a Q&A live stream once, someone just talking about themselves and not even playing a game, and a viewer donated $500 to have their comment promoted. And this was a stream from a 30 year old dad, so I can imagine that female streamers who promote their sexuality get these kind of donations far more frequently.
A lot of creators also rely on Patreon now, which is a website that allows fans to pledge a monthly donation, often in exchange for exclusive content. It's usually a tiered system, so for example: $5/month will get you access to an exclusive stream, and $50/month would get you a personal shout out and maybe some merch etc.
IG models have also started utilizing Patreon- I've seen girls who will release exclusive photoshoots for Patrons and things along those lines.