It's not always easy to stand up against someone who's been living in a place longer then you have. It's as if you're lower down on the pecking order because you came last, and maybe that's what gives J the imaginary belief that she can boss you around.
What Gala Girl said about the broken record is really spot on. You need to think of some phrases or really, just some verbal self-defense sentences, to use against J when she tries to tell you what to do. Keep repeating them. The repetitiveness of what you're going to be telling J is going to sound strange to your own ears. But keep it up. It may even infuriate her (and yes, making someone mad is probably the last thing you want to do, but short of making her violent, you'll want her to know that you are firm in your beliefs and will not back down). Eventually, she will start to respect you.
The alternative is to allow what's been going on to continue, or maybe even get worse. So if you're going to do this, do it sooner then later. The longer you wait, the harder it's going to be to change her attitude about you.
Take the risk of thinking for yourself, much more happiness, truth, beauty, and wisdom will come to you that way. - C. Hitchens
Me: Male, bi, 48, flexible