J.S.
I have an 18 month old little girl myself. While I am lucky in some sense that she doesn't really care for TV (I have tried in a pinch a couple of times when I really needed to get some things done, yesterday was the very first time she ever watched it for more than a minute or so) I think you just have to keep enforcing what you know is right. Let her watch a set amount of time then turn it off, pick her up, and go play somewhere else.
As to what to do all day...your day sounds like mine. My daughter is just now getting to the point where she will play some on her own. I personally get bored during those days where we have nothing scheduled. My daughter does mother's day out twice a week plus my gym on fridays. I just figure it goes with the age/stage she is at. I don't have much advice for you. I just wanted to say, I'm in the same spot as you.