Legal Question in Wills and Trusts in California

If it is revocable, your mother is the initial trustee. She can name both of you to act jointly as successor trustees of the trust. That's not always the best way to do things, though, unless she writes in a dispute-resolving mechanism in case you and your sister don't see eye-to-eye on everything. And don't believe it won't happen! I've seen too many cases in which one or the other gets greedy.

It is advisable that she also create a pour-over will, even a simple one, because property might come into the estate even after she passes away. For instance, a rich aunt might somehow will property to her. Where would she want it to go if she doesn't have a will? There are laws that specify intestate succession (how property is divided if there is no will), but it's easier to be certain than uncertain. A pour-over will simply "pours" such property into the trust, and is then divided as your mother has specified in the trust.