7 Answers

Then you need to leave. It is her house. Maybe she can no longer afford to pay the extra in electricity  or any other bills you may have added to.  Did you work and save money during all those years of free living? Why do you think anyone owes you anything? Your life, your daughter, provide for her and yourself like millions of people do all over the wold. 

Has your mom ever gotten mad and told you to leave before now?  For what reason does she want you to leave?  If you were in your mom's shoes, what would you want?  Why should you be allowed to stay?  Is there something you and your mom can agree on that will allow you to stay?
There are many questions to consider here, as this is a personal issue as well as a landlord-to- tenant issue.  It sounds like you had a verbal, open-ended agreement.
Depending in what state you live (or country if not US; I keep forgetting there are friends here from all over the world), you may be able to squat there and be a pain in the butt to your mom while she jumps through the legal hoops to get you out of there; it could take months.
OR, you could sit down with your mom and find out exactly what she wants to do with her house.  If you can make that happen for her, perhaps you can stay. 
IF ALL ELSE FAILS: 
IT'S HER HOUSE.  SHE LET YOU STAY THERE FOR FREE.  DO YOU REALLY THINK SHE OWES YOU ANY MORE THAN THAT?  CONSIDER YOURSELF BLESSED, CLEAN THE PLACE THOROUGHLY AND FIND YOUR OWN PLACE.

How much do you think your mom owes you? Judging by your question you have lived rent free at your moms expense for some years.I would say she has done her bit.Find a place of your own & move out.Give your mom a chance to get on with her life.

Have you got a legal agreement between you & your mother?

The old expression applies here ,YOU DON'T HAVE A LEG TO STAND ON . Its sad that the granddaughter suffers in this ,but thats life .  Arrange for a good cleaning and a exit with dignity and get on with your life . This is the downside of dealing with family ,no lease , no written agreement ,no contract means = NO CHANCE !!!  Everything in writing each time all the time or this is where you end up . This is the equivalent of being in a very cold stiff wind with your drawers down  ,out house in 40 below weather . Try to protect your life and shelter better in the future . Wish there was better news but sadly no .                               Bill

It's your mom's house and rent or no rent still makes you a tenant. Perhaps she should go the legal route to get you out but it is her right to do so. Have you discussed this with your mom? Is the feeling mutual? Perhaps, through talking, something can be worked out at least time wise. My feelings are that you should honor your mother's feelings as well. Leave on a good note so this doesn't come back to haunt you......

Since there was no formal agreement signed, the best you can hope for, under most state laws, would be treated like a holdover tenant.  Such holdover tenancy is akin to month-to-month commitment, and you could be asked to leave within 30 days' prior written notice.  If you haven't vacated by then, the owner of the house would then go to court (takes about 7-10 days) to ask you to vacate.  After the judge agrees to the eviction, you might have up to 28 days to vacate the premises.  The way I see it, you could have up to 2 months or so.