I was matched with a family for a live-in situation. I was told that it would be "ideal" conditions but my quarters are a small suite over the renovated garage. It gets very cold at night, I don't think there's any insulation or heating as they supplied a plug in heater. I don't have a stove and only a hotplate, microwave, bar fridge, and minimal counter and cupboard space. It's very minimalistic and uncomfortable. There's no space to have a friend over. It's a bed, couch, and table crammed into a room with small bathroom shielded by a curtain.
The agency assured me that I would "part of the family".
This sounds like a bad match. With the exception of the heat issue, some nannies would prefer this set up over having a room with a separate exit and no expectation that any of her off hours would be spent with the family. You can't depend on an agency to make a good match for you anymore than a family can fully trust the agency has thoroughly checked references and made a good match for them. Agencies make money by matching quickly and since its more difficult for live in nannies/live in employers to replace a bad match, bad matches are less riskier for the agency.
In the future, you should make sure to ask enough questions during the interview to understand whether the position is a good match for you. This includes not just answering question but asking a few on your own. As a live in, its also pretty reasonable to ask for pictures as well as a description of the living quarters.