Wow! How old is this child she is bf? If she is expecting #2 than I would think the older one would use a sippy or a bottle. I would possibly explain that it is difficult to do what she is asking and she should try to bring frozen or pumped breast milk for you to serve/feed the child. Where do you live? Can't she just hang outside on the porch or in her car?!?!?
I am TOTALLY kidding about that! Wish I had some useful advice. It sounds like a tough call either way. I've had bf babies, but mom's always pumped and brought frozen or ready to eat milk for the babies. Good luck!
As far as using your bedroom, I would just say it is a habit you would rather not get into and leave it at that. You shouldn't have to explain not wanting to loan out your personal space.