Watching Shassi spiral down to the end of her life, this question is of more import to me than would otherwise be the case! According to Norma Hornung’s initial research, it’s around 13-14 years. You can help Norma gather more information about Shiba lifespan by going to this link, as she is asking for data related to Shibas who have died in order to gain a better understanding of how long our breed tends to live.
I am so sorry to read about Shassi. I know how hard this must be for you. Please know that you are both in my prayers. Try to remember all the good times you and she had together.