I have a client who passed away and has a living trust naming his sister as the trustee to settle his affairs.  His sister is a resident of and citizen of Canada.  The client was a US resident and US citizen living in California.

When preparing his 2022 tax return, form 1310 asks for the social security number of the person claiming his refund.  However, the sister does not have a social security number since she is Canadian.

Does she have to apply for a social security number before my client's tax return can be filed?