OP, I think part of the difficulty in this discussion is that you've presented all of the things that annoy you about this tenant as being equal and they're not, which is part of the confusion about whether or not posters agree with you.
The only truly egregious thing tenant has done in my opinion is to take your headache meds without asking and it's perfectly reasonable for you to talk to her about that, even point out that the reason that you are taking in a boarder is to make some extra money so having to spend more money to replace medication doesn't make sense.
The just-met romantic interest spending the night, using an electric heater that would substantially raise your utility bill, and bringing home a kitten (ooohhh, kitten
) are also things that are certainly reasonable for you to veto but the point is she asked you
(assuming here about the kitten). She didn't show up with new guy and wander back to her bedroom, she didn't just buy a heater and begin using it, and she didn't (presumably) show up with a kitten, she talked to you about it first and that's absolutely the right thing - since you say you really didn't have rules set when she moved in, that's the way to negotiate them.
Thawing meat and letting the blood spill on your food, definitely worth a discussion. The dishes? Several people here have made other suggestion that might be useful.
I already talked about some of your other comments in a previous post, the only thing I'll add is that I am unfamiliar with the idea that a lodger would only have access to common areas part of the time, but that may be a difference between the U.S. and Australia.
Bottom line...read the title of your thread: "To share or not ... that is the question" and consider if you really want to share, not just your blanket but your house.