term definiton-joint tennants with rights of survival

I live in Mass. and have a question relative to my mother's investment account. I am the only heir and am named on her investment account as a jt tn. I need to make sure her portfolio is protected in case something goes "sour" with my finances. Please advise the meaning of this term and if this protection is in place for her. thanks
rudd

Joint tenants with right of survivorship means that at the first death the assets in the account automatically go by operation of law to the survivor(s).