The alleged victim, who we are calling Mrs A as she can't be named for legal reasons, reported the assault in February last year.
But she was left horrified when she was told the case had been dropped due to "insufficient evidence".
And it was only when she appealed the Crown Prosecution Service's decision, she discovered Beds Police had actually "MISPLACED" her samples.
The CPS review told Mrs A: "As the samples taken from you by police have been misplaced, we are now unable to obtain any evidence to show what you suspect happened was in fact actually the case."
Her solicitor Matthew McConville, who specialises in sexual assault cases for Irvings Law, called the force's conduct "terrible" and fears more people could be at risk by police failings.
"She trusted the police. It took her a few days to gather the courage to report the crime, but when my client did, she was completely let down," he said.
"The police's conduct has been terrible. This client has been sexually assaulted, gone through the intrusive process of giving samples, recalling the events of the assault, and gave interviews. But to then be told there is no further action without a reason, you can imagine how that would impact upon her.
"I want to bring it to the attention of the Bedfordshire region that there might other people who have been affected by this but are completely unaware of police failings."
Following her complaint to Bedfordshire Police in May this year, the force apologised to Mrs A, who has been receiving counselling, for misplacing the evidence.
However, DCI Jackie Dadd said the victim's sample, which was later discovered, wouldn't have made a difference to CPS dropping the case.
Mr McConville claims freezers where samples were stored was at capacity and not kept in any type of order, and his client's sample was only found after police reviewed its contents.
"There is no doubt the failing by the police would have made any psychological symptoms from the incident worse and she is currently undergoing counselling," he added.
"If my client had never lodged the complaint she would have always been a victim and it would have been a lost charge.
"But because she stood up for herself and challenged them they then decided to reopen the investigation which hopefully will result in a prosecution."
Following CPS' findings and Mrs A's complaint, Bedfordshire Police apologised for its handling of her sample - and have reviewed their documentation process.
DCI Dadd said: “While I’m satisfied the officer assigned to this case carried out a thorough and detailed investigation, I do accept the handling of some of the samples in this case fell short of the service level we aspire to.
“The sample, which had been taken in order to establish whether the victim may have been drugged, was subsequently recovered as a result of a robust review into our exhibit documentation process."
But DCI Dadd said after careful consideration on advice from experts, it was decided Mrs A's sample would NOT have made a difference to the CPS decision to drop the case.
“The matter was referred to, and thoroughly scrutinised by, our Professional Standards Department, and some organisational learning identified which has already been put into place in the form of a new force policy to strengthen our exhibit documentation process.
“I would like to take this opportunity to apologise to the victim for the handling of the sample in this case.
"I would wish to reiterate that we will always place the highest priority on the investigation of reports of rape and sexual assault, and ensuring the provision of appropriate support for victims.”
If you think or feel you may have been affected by Bedfordshire Police like Mrs A, contact solicitor Matthew McConville on 0151 475 1999 or [email protected]