Hey, are you still here? You do know the party was last weekend, right?
No, no, it's really alright. I absolutely don't mind if your mother stays for another three months.
Other than lying, having a house guest overstay their welcome and place a strain on your familial bonds is a tricky situation to get out of, at best. Mothers-in-law, fathers-in-law, well, any in-laws really, as it wasn't them you married, and they see you as the one who took your spouse away from them, changed them and caused the ruination of mankind.
Well, we do tend to go overboard on the long-standing in-laws overstaying their welcome routine. If the relatives asked if they could "stay for a while", then anything goes, and asking them to leave would probably go like; "when was it you said that you would be leaving? The reason I ask is that we were planning on taking a trip...". Well, sometimes taking an impromptu trip is worth the cost.
Mother-in-law jokes notwithstanding, the average male would much rather not have their wife's mother in the next bedroom, or, for that matter, in the same home every single night for an extended period of time. Things change, and moods are altered when one of a couple's parents are staying over for, well, way too long. The problem can sometimes be getting your spouse to realize that their parent(s) is/are overstaying their welcome. Once they do realize it, and the effect it is having on you, they should be sympathetic and kindly ask their parent(s) to leave.
If the guests who are overstaying their welcome are not relatives, nor very close friends, and are causing a financial burden by eating your food, drinking your liquids and alcohol, and using your utilities, then asking them for a share of the living expenses might just see their back ends running down your driveway. The thing about hangers-on is that when they are asked to pony up their share of the costs of living, they usually move on to their next relative or friend. If they say that they will give some money in a week or two, when their expected money will be in their account, do not believe them for a minute.
If the guests who are overstaying their welcome are good friends who are down on their luck, lost their home to the foreclosure fiasco, and/or lost their jobs due to factory closures or company downsizing, then asking them to leave or chip in will be a very hard thing to do. If you have a strong moral compass, you would find it very hard to ask these overstaying guests to leave. It would be much like asking your orphaned nephew, who just got back from his fourth tour of duty chasing terorrists in Afghanistan to leave.
Using your best judgment, you decide if the financial burden is worth keeping the friendship. If you simply can not afford for them to stay, as in you would have to cancel some bills, skip a mortgage payment or car payment, then explaining the financial burden that they are causing you should shame them into leaving, if they can not afford to chip in some money for their expenses.
It's a tricky situation, and sometimes no matter how you handle it, you will become a pariah in their eyes, and even the eyes of the rest of their family and friends. Good luck with your choice.