Ms Russon's mum Anna Certowicz said police "didn't seem to think it was worth investigating".
Police have said they cannot comment while an investigation is pending.
Newport West MP Ruth Jones said she understood the "consternation at the delay in apparently finding them" but people "need to hold fire and wait".
In a statement, South Wales Police said the group was the subject of inquiries "by Gwent Police following a missing person report made during the evening of Saturday 4 March".
"A subsequent missing person report in respect of one of the individuals was made to South Wales Police on Sunday," it added.
Gwent Police, which was responsible for the search, issued an appeal for information on the missing group on Sunday night, a few hours before they were found. South Wales Police is investigating the crash.
Friends of the five claimed they found the vehicle but police have said it was located by a helicopter.
Police have said they cannot comment while an investigation is pending.
Newport West MP Ruth Jones said she understood the "consternation at the delay in apparently finding them" but people "need to hold fire and wait".
In a statement, South Wales Police said the group was the subject of inquiries "by Gwent Police following a missing person report made during the evening of Saturday 4 March".
"A subsequent missing person report in respect of one of the individuals was made to South Wales Police on Sunday," it added.
Gwent Police, which was responsible for the search, issued an appeal for information on the missing group on Sunday night, a few hours before they were found. South Wales Police is investigating the crash.
Friends of the five claimed they found the vehicle but police have said it was located by a helicopter.
Cardiff car crash: Mum criticises two-day search to find group
Family and friends question why it took two days to find five who went missing after night out.
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