Presidents don't attend First Lady funerals. When Mrs. Reagan died in 2016, both George W. Bush and Bill Clinton attended as former Presidents but Mrs. Obama represented the White House. Likewise when Betty Ford died in 2011, Mrs. Obama represented the White House and the President didn't attend. When Lady Bird Johnson died in 2007, former Presidents attended but Mrs. Bush represented the White House.
So while there is not any love lost between the Bush family and Trump, the fact that the President is not attending has nothing to do with that. It's all protocol.
Thank you for this info on First Lady’s attending former First Lady’s funerals. I had not known this.