I definitely get the feeling that we see Joyce from Buffy's perspective a lot of the time, and how it's frustrating how little her mother can understand, but I also got the sense that the shows view of Joyce was that she was a great parent and that Buffy was at an age where she couldn't fully appreciate how hard it was for Joyce having to deal with her as a single parent.

But when I started really thinking about those seasons when Joyce wasn't in the know of what Buffy was really getting up too, there still isn't all that much reason IMO to act so long-suffering about what trouble Buffy is going to get into next. We really don't get much indication of what she's so upset about, in Bad Eggs for example she basically just catches Buffy dressed in her room (not sneaking in or out), and then not being in the library when Joyce goes to the school. Of course the audience knows that Buffy was out slaying and couldn't tell Joyce exactly what she was doing, so from that perspective we are invited to sympathise with Buffy, but was there really any reason for Joyce to get so mad over Buffy not being in the library at the school, even without knowing about Buffy being a slayer? It's not like she caught her cutting school to go out shopping or something, she was still actually in the school building and trying to say that well yeah but there was a gas leak, but apparently that was enough for Joyce to completely cut her off and say that you're now confined to your bedroom indefinitely? It just didn't seem like the writing really backed up why Joyce was getting so frustrated with Buffy's behaviour