Would she really put tape on your niece? She doesn't sound like someone I'd want to leave my kid with between that and the car seat.

You're right, you have nothing to feel guilty over. You set a nice boundary by telling her that you were going to stay home instead of going out with her. Someone on here once recommended a book to me called 'Boundaries' by Cloud and Townsend. The book is religious. I'm not religious myself, but I got quite a lot out of the book anyway. Another good book is 'How to say no without feeling guilty.' Boundaries are hard, especially when we were brought up with mothers who had no boundaries which makes a lack of boundaries seem normal to us. As you set more and more boundaries, the guilt starts to go away but it can be really hard at first.