The legal document that would accomplish this transfer is a deed. Be very aware, however, that there may be strong reasons to NOT deed the house even though she thinks it would be a good idea. For a full discussion of the pros and cons, your mother needs to consult with an experienced elder law attorney. If she does not know one, use the attorney-finder at www.naela.org.
Best wishes for a favorable outcome, and please remember to designate a best answer.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.
As the prior answer mentions there are good reasons not to transfer property away from your mother during her lifetime. Concerns about who will own property following death are best discussed with a local attorney who is familiar with your state's probate laws. There are likely simple and inexpensive ways to insure that you will be the owner of the home following your mother's death without incurring the unintended consequences of a lifetime transfer.