Letters Testamentary will arrive after tax day

My mom died in December and I had my probate hearing on March 25. I'm just waiting for the letters testamentary to arrive in the mail, which my lawyer says will take about 3 weeks from the hearing. I'm filing form 1310, which requires the court papers naming me executrix. Since I can't e-file her return, I won't have the letters in time to mail with the return. Any advice?