An acquaintance is eager to attend a symposium in my town. She told me that she does not have enough funds and would like to stay with me. I honestly do not have space for her. On top of that, I live in an academic community in which we have housemates.
The person seems to insist and has implied that she is willing to sleep on the floor if necessary. Is it rude to make plans to travel when you cannot afford it? Should I just tell her she is rude? Should I consider having her stay even if it is on the floor?
If you do not feel comfortable having an acquaintance stay at your home, then do not let yourself be coerced by her.
It is rude to self-invite or to insist upon staying at a place when the host has politely refused the request. However, no matter how deserving, it would be impolite to point out her rudeness.
Because you have a housemate, you could say that you have an agreed upon policy with your housemate that there will be no overnight guests. Then, just leave it at that. Or, you could say that you are sorry, but you cannot accommodate an overnight guest. You do not need to go into any more details or explanations.
If the acquaintance keeps insisting or bothering you, then you are under no obligation to continue the interchange with her.