Jaqueline McQuade saw her daughter Erin McQuade and her parents Jack and Lorraine Sweeney die as a bin lorry lost control in central Glasgow on Monday.
Archbishop Phillip Tartaglia led a special memorial mass at the city's St Andrew's Cathedral on Wednesday for the six people who were killed in the incident, and all those affected.
In his homily, he also says he spent time with those others who'd lost their loved ones, just hours after the crash on Monday.
A 14-year-old girl injured in the incident remains "serious but stable" in hospital. Four others are in hospital in a stable condition.
The driver of the lorry is also continuing to receive hospital treatment.
Speaking of Jaqueline McQuade at Mass, Archbishop Tartaglia said:
"She had seen her daughter and her own parents killed almost right in front of her.
"Can you imagine the horror? Can you imagine her sadness?"
Detective Superintendent Andy Gunn, Senior Investigating Officer, said on behalf of Police Scotland today:
"The events in Glasgow on Monday were devastating - for the families and friends of the victims who lost their lives, for those who were injured, the local community and beyond.
"I would like to reiterate that there is nothing to suggest this was a deliberate or malicious act.
"However, there is a significant police investigation ongoing into the circumstances which led up to the crash, which claimed the lives of six people. Our thoughts remain with the families of those who have lost loved ones as a result of the incident.
"Police Scotland is continuing to support the families of those involved.
"A dedicated team has been assigned to this investigation, including specialist investigators and highly experienced detective officers from Greater Glasgow Division, Specialist Crime Division and road collision investigators.
"The investigation will be thorough and exhaustive as we gain an understanding of the circumstances of Monday's events and will continue in the coming days and throughout the Festive period.
"The investigation will take as long as is required and we will ensure all lines of enquiry are investigated before we report to the Crown Office and Procurator Fiscal Service.
"I would again like to take this opportunity to ask anyone who has any footage, from mobile phones or other equipment, to email the dedicated email address email@example.com as it may assist with our investigation."