Your clarifications do help.
She is not on the lease, right? She is not paying half the rent, half the utilities, Internet, cleaning/household products, half of anything, correct? She is just paying for a room.
You are effectively her landlord. It's unfortunate that you did not, when you first put the room out for rent, stipulate a strict house rule that there are no overnight guests allowed (or if you prefer, no guests at all) due to the very small size of this apartment. I think you have that right, since you are renting just one room and the renter doesn't pay half of anything, just 1/3 of the basic rent price (or maybe a third of the utilities too, but still...).
I also assume you have a child, probably a small one?, in this apartment with you, husband, renter and renter's boyfriend. That, right there, would be the deal-breaker: Do you want this boyfriend, or any other boyfriends or renter's friends whom you have never even seen, walking around your home, sleeping there at times you can't predict, coming in drunk -- when there is a child in this close-packed household?
I think you know the answer to that.
What lease arrangemnet do you have with her? Is it written? Does she expect to have, say, a one-year lease? If I were you I would look at either telling her she has to move out when her "time" is done, or if that is far away and/or you don't have a real "end date" on a "lease" with her, I'd tell her that she has X weeks to find a new apartment. You do not have to give her a reason unless YOU want to do so. Just tell her that you need the space or something like that. If you have a formal, legal, written lease, of course, things are going to be tougher.
If you can get her out, I would look into ways to do without a renter, but if you must have one, you need to do two things: Check that person's background (I hope you did it with her -- you don't want someone with a criminal background in your home where you and your child are, right) and issue written rules that state no guests, ever, period. With consequences: One time is a warning, second time -- eviction. Just say that with a child living there you cannot have strangers coming and going. They may not be "strangers" to your renter but they ARE strangers to you, and you can insist that they not come into your home.
It sounds, though, as if you might have trouble working even if you have a perfect renter with zero guests, ever. I would try to see what you can do to avoid needing to rent to someone, though that sounds very difficult from what you describe.