In the back of her mind, she knew the chances were slim-to-none, but she held out hope anyway.
Then, earlier in 2012, she received a letter that finally confirmed what she long suspected: Private First Class James J. Jacques did not survive the crash.
On Monday, the remains of Jacques arrived in Denver in front of Denver Police officers, TSA agents and a host of fellow Marines.
"Thanks to God he's home now," Guerra said. "At least now we'll have closure."
On Tuesday - on a day that would have been Jacques' 56th birthday - his family will watch as Jacques is buried with full military honors at Fort Logan National Cemetery. There are so many members of Guerra's family who never got to meet Jacques, but they plan to attend.
"We would never let them forget that they had an uncle," Guerra said.
Jacques was 19 years old when he boarded a helicopter bound to rescue SS Mayguez - a Khmer Rouge-captured U.S. merchant ship. President Gerald Ford called the act "piracy."
On May 15, 1975, the helicopter was shot down.
"For years, we thought maybe he was captured ... or maybe someone had taken him in," Guerra said.
While the remains were recovered in 1995, it took until 2012 for the Joint POW/MIA Accounting Command Central Identification Laboratory to positively identify the remains as Jacques.
Guerra described her little brother as outgoing, athletic and an occasionally-ornery teenager who grew up determined to join the Marines - even as the war in Vietnam was coming to an unpopular end.
"He was just a good kid," Guerra said.