What can I do to take action against her, I need some kind of advise before it's too late.

This question is best answered by probate attorneys. You don't say if your mother had a will or if she died intestate, If she died intestate, then most likely the house would be split among your siblings.

You need a lawyer. You do not say whether your mother's estate was ever probated. If your sister took title to the house through a probate because she was named in a will then it is her house. Otherwise, you may well have a claim to the house. If the estate was probated and all five of you own the house together you need to file a partition action to get your value of the house. Five adults sharing a house doesn't always work so well. See a lawyer so you can figure out where you are. Good luck.

In the absence of a will or a deed signed by your mother during her lifetime giving the property to your sister, she cannot just "claim" it as her own. You do not say if your mother's estate was probated. If it was, the house should have been distributed as part of the probate process. If your mother had a will, her will would control, and she can give the house to whomever she pleased. If your mother did not have a will, and presumably no surviving spouse, it would go to all five of you equally. The bottom line is your sister cannot just claim the house as her own. Once the proper ownership of the property has been established, if all five of you do own the property together, it does sound like a partition action is warranted. You should contact a local probate attorney to discuss the matter in more detail.