Re: Property
Here's the rest of my answer:
Another possible approach depends upon how the acquisition cost (down payment and cash closing costs) of the property was shared. If your sister contributed to the cost, she is an equitable co-owner and can obtain full legal co-ownership by bringing suit to quiet title in herself, notwithstanding that her name is not "on title" down at the recorder's office. She can, if she chooses, also sue for partition of the property if she can establish co-ownership. Partition is a process whereby the court directs the sale of co-owned property and, after a sale, the distribution of the net proceeds of sale to the co-owners in proportion to their ownership interests, after adjustment for excess advances by any co-owner for expenses such as mortgage payments, property taxes, insurance, necessary repairs, and the like.
Note that Code of Civil Procedure section 872.730 makes partition proceedings available for division of partnership property in a suitable case.
Oral agreements to transfer interests in real property are not enforcable EXCEPT as described above OR if you can show part performance or what is called "estoppel," and you might be able to plead either or both.
Finally, if your sister cannot establish any ownership, either as a partner or as a co-owner by virtue of investment, or by estoppel or part performance (which I would find surprising based on your facts) there is still a hope, based on the law protecting a good-faith improverof property owned by another, Code of Civil Procedure sections 871.1 et seq.
Depending upon what causes of action are employed and what claims for relief are made in a lawsuit, it may be possible to file and record a "lis pendens" (notice of pendency of action) to prevent sale of the property while your sister's rights are being adjudicated.
I'll be pleased to give you a free full consultation upon request, if you can supply a few more facts such as whether your sister contributed to the down payment. Please contact me directly.