Does a tenant’s rent increase if their partner moves into their room?

I am renting a house with three other tenants. One of them wants her boyfriend to move into her room with her. It is agreed we would split the bills 5 ways now, but she doesn’t think her rent should increase. Is there a standard procedure for situations like this?
Update: The rent is different for all of us based on room size and room attributes such as air conditioning. Obviously, I am not concerned about how her and her boyfriend split the room's rent or anything concerning bills but rather does the mere fact there is an extra body in the house justify raising HER room's... show more The rent is different for all of us based on room size and room attributes such as air conditioning.
Obviously, I am not concerned about how her and her boyfriend split the room's rent or anything concerning bills but rather does the mere fact there is an extra body in the house justify raising HER room's rent and lowering everyone else's?
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