Hope I have my timeline right. The bombings took place on the 15th and
Thursday, April 18
5 p.m. ET: The FBI releases pictures of two male suspects being sought in connection with the Boston Marathon bombings.
http://www.cnn.com/2013/05/01/justice/boston-marathon-timeline/
But he wasn't missing from 15th to 18th. He was living as normal at the apartment. I believe the claim is on the 18th she either dropped or left child there to babysit. Also on the 18 she reportedly saw him on TV and called him. So, if she didn't see him at home in the eveneing of the 18, she clearly knew he was suspected of terrorism, so she wouldn't have been surprised.