Rebecca Coggins said she was told by police this morning that they were now treating Natalie's disappearance as a murder inquiry and had discovered something 'significant'.
Officers began digging up graves at a cemetery metres away from Natalie's home this morning - four days after her image was shown to millions of viewers during a performance by the Missing People's Choir on Britain's Got Talent.
Ms Coggins, aged 40, said: "The police called me this morning, they told me it was now a murder inquiry. They said they had discovered something significant. They said they are looking for a body, there is nothing to suggest she is still alive."
"They are giving me a police liaison officer. I'm waiting to hear more on what is happening this morning.
"I just feel completely numb. Absolutely heartbroken, I have cried so much this morning I have no tears left now. I have now got to rally my family around so we can grieve together."
The family was shattered when Natalie failed to return home, having apparently gone to the shops. She left without her 11-week-old baby Rhys and did not take her mobile phone or any other possessions.
Ms Coggins added: "I always hoped she was still alive. I never wanted to get that call this morning. I'm in so much pain, people are now waking up to this, it is just so, so hard to take after all we'd hoped for, we believed we might see her again."
"The showing of her picture on Britain's Got Talent may have sparked this new information. Someone knows something about her disappearance."
Regarding the appeal on Britain's Got Talent, Detective Inspector Tom Chisholm from West Midlands Police said: "It is fortuitous, I'm aware it was on there. It did the same thing we are trying to do here today, raise awareness and help us appeal for fresh information. We want people to come forward."
Natalie had been with a friend the day before, returning home at around 9am and stayed until noon before heading out again, and hasn’t been seen by her family since.
Sightings were reported across the country, from Bournemouth to Scotland, but her loved ones are no clearer on what happened to Natalie.
Since the day she went missing her bank account has remained untouched. The last communication she made was a voicemail on the day suggesting she was planning to visit friends in Tamworth.
The case was re-energised four years ago when police dug up a paddock in Himley where Natalie kept horses but the search proved fruitless.