I think there should be some fluidity with boundaries, because the whole idea is to help you create your own, not adapt to someone else's. However, it's the T's job to ensure that the boundaries are being maintained appropriately. You can't just suddenly change the rules all at once like your T did. It seems like she panicked and you paid the price for it. It's much like deciding you're being too lenient with a child and going from permissive to authoritarian literally overnight. I don't think I need to explain what kind of hell you're in for if you ever try that one btw...
I think it can be hard to be completely clear with the boundaries though. Realistically, they are going to change depending in what 'developmental level' you're at in therapy at any given time. As with kids, the younger ones need more solid rules than the older ones.