When she comes to see you once to twice per week, that is without her husband right? So when she goes home, maybe she just wants to spend quality time with her husband without interruption.

She is already coming out to see you one to two times per week. I think that may just be her limit.

Now, her not wanting you to call to check on her when she's out sick, that's a bit strange. But if that's what she wants, then I guess you just need to respect her wishes. You may also want to try being friends with other people if this friendship causes you confusion.