Ahh it's the subtle digs that you look petty for pointing out... I know all about that.
People telling you you're being unreasonable but it all adds up.
You're not being unreasonable though.
Is she living with you? If so, perhaps it's time to give her notice. Does she have a key? If so change the locks. Tell her she needs to give notice before popping over and keep the doors locked. If you're not in the mood, tell her now isn't a good time. If she starts cooking stuff, stop her before she starts. If you miss the start, tell her to take it home or turn it off. Tell her to do her dishes before she leaves, give her a call remind her he forgot to do them (so she doesn't get away with it).
If ANYONE pops by and you're not in the mood, tell them now isn't a good time, they should have called. Do NOT let them in the doorway, step outside for a second if you have to.
As for people staying over, if you're not asked tell them yuo weren't asked and it's not convenient. If you ARE asked, tell them it's not convenient.
Essentially, you just need to start to feel stronger. People won't like it at first, they'll resist the change from getting their way all the time to not, but they'll adapt.