In Buffy the Vampire Slayer, season 5, episode 1, Buffy vs. Dracula Dracula gets into Buffy's house and bites her.
We learn that Joyce invited him in.
While Tara and Willow are performing a spell to keep Dracula out of Buffy's house:
JOYCE: I'm not like this. I don't invite strange men over for coffee, it's just ... Oh, when you girls are older you'll understand. (Sits on stairs) It's hard to date. Sometimes you just ... feel like giving up on men altogether.
Willow and Tara sneak little looks at each other and try not to grin.
At this point in the series, Joyce is not aware of Willow and Tara's relationship.
However, later in the season,
Does Joyce learn of Willow and Tara's true relationship before that event?