Wendy herself had also had abnormal cells at the age of 25 and she had received successful treatment.
But tests showed that at Cathy's cells had already developed into cervical cancer and had started to spread around her body.
Despite having chemotherapy treatment, Cathy, a mother of two, was unable to fight the disease and died, aged 25, in February last year.
Now Wendy is campaigning for the age of cervical smear tests to be lowered as she says if Cathy was tested earlier than 25, the disease may have been caught in time.
Wendy, 46, who lives in Stoke on Trent, Staffordshire, says: "Now we are campaigning for a change in the law to lower the age for smear tests from 25.
Girls should be having them as soon as they are sexually active. How many more mums need to lose their daughters before the Government does something?
"We don't want her death to be in vain. Her children may grow up without their mum, but we don't want this to happen to anyone else."
Cathy had her first smear test in August 2010. She had suffered bleeding after she had given birth to her first daughter, now five, but hadn't gone for a check up because she was below the age of 25 and wasn't eligible for a smear test.
The results of her smear test came back showing abnormal cells in her cervix.
"It really was like history repeating itself for me, as I'd had abnormal cells after my first smear test at the age of 25," explains Wendy.
"Cathy was worried but I told her not to as I'd had laser treatment and then been given the all clear and I was sure that was what was going to happen to Cathy too."
But more investigative tests a few weeks later revealed that she did have cervical cancer.
She rang me crying down the phone to tell me that she had cancer. I started crying too. It seemed so unfair. She had two little girls aged five and three.
"Were they going to lose their mum?"
She and fiancé Alex Bates, 26, made plans to get married and she celebrated Christmas Day with her family.
But just four days later, Cathy had agonising pains in her stomach. The doctors initially thought it was scarring from the radiation treatment but after several weeks she was struggling to eat anything.
Scans showed that the cancer had spread to her stomach.
"We were all devastated. She'd beaten the cancer once, only for it to come back in her stomach," explains Wendy.
Doctors told her that it was a very rare cancer, linked to cervical cancer, and they said they didn't know how long she had left.
Cathy wanted to get married, but she was too ill to say the vows, so instead a vicar blessed the wedding rings and Alex said both their vows.
"It was heartbreaking. Cathy had gone downhill so fast. She managed to slide the ring onto Alex's finger, and just a few hours later she passed away.
"I couldn't believe that I had lost my daughter like this. Only a few weeks before we thought she had beaten the cancer. But now her life as a mum and a wife had been halted by this cruel disease."
Wendy is now campaigning for a change in the law. Cervical cancer screening has been limited to women aged 25 and over since 2004 because so few under-25s were found to have the disease.
Local health trusts cannot lower the age limit until the Government changes national policy.
"Cathy had a smear test as soon as she was eligible to do so, but her death has made us realise that there must be 17 and 18-year-old girls out there who may have cancer and don't know about it," says Wendy.
By the time they have waited for a smear test, it could be too late.
Wendy is now backing a campaign to have the age of smear tests lowered to 20, which has already attracted a 20,000 name petition since being started by relatives of 23-year-old Claire Allan after she died from the disease in 2009.
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