Maybe I misunderstanding but to me, an assistant assists. When she came, she likely expected same (other than appointment times which were clear she would be alone). I think if I went for job as assistant, I would not expect be doing all while my boss does non-work related things. It fine you doing that but it could be she not expecting to do it all unless you physically not there and I think it reasonable assumption.
Afterall, if she going be left doing it all, then she might well open own dayhome.
She might have viewed this as safe, small environment where she can find out if this field she want work in and maybe never expected to be running alone other than odd time for short time.
She might have taken role because it small home, no responsibility, and not primary carer.