I think that depends on what your role is, and how much time you are prepared to give. I was an assistant cub leader for a few years, I went to weekly meetings, planned the odd meeting, went on camp once a year. But I'm now the main leader - I have a great team of assistant leaders, and we do much more than we did when I first joined. So it's now several hours a week, plus several weekend trips and camps, planning meetings, trustee meetings etc.
However, I have an assistant leader who attends every other week, due to work shifts. I have an assistant leader who attends every week, but doesn't do much else. We have trustees who come to the trustee meetings, but don't really do much else. And that's all fine. People give what they can, and if they can't (or don't want) to give more, then that's a case of setting their boundaries, and other people respecting that.
In the OPs case, it sounds like the boundaries have got a bit blurred. She needs to reset the expectations of the other members by putting in clear boundaries, giving what time she can, and then sticking to it.