Joy Watson was attending a dementia awareness event at Lighthouse Christian Centre in Eccles earlier in the week but she was told she couldn't enter the main room with her dog because food was being served to 160 people there.
Mrs Watson (below) was with Demy, a young Labradoodle training to be a dementia dog.
She told Manchester Evening News: "I walked into the foyer and was told in a very abrupt manner 'you can't bring your dog in here'.
"I had to take Demy to a dog day care centre in Trafford, and then return to the event.
"Later in the day I approached a pastor from church and asked why they would not let the dog in.
"I found it upsetting. I spend all my working hours trying to get rid of the stigma attached to dementia, and this incident was a backward step."
Lighthouse Christian Centre has said under health and safety rules it could not allow Demy into the room and that it "very respectfully" asked if Joy could keep it out.
One of its pastors Alex Robertson told the paper: "From what I understand Joy wasn't asked to leave the building only to stay out of the main room with the dog where food was being served to 160 people.
"We are always trying to be as accommodating as we can.
"We don't come down hard. But we have to keep the conference within hygiene rules and regulations."
Corin Pilling, from the Christian disability charity Livability, told Premier's Big Breakfast: "People with disabilities and people living with dementia - our Church is incomplete without them being in there... they have something unique to bring to the body of Christ.
"People recognise that churches can't do everything but it's often about attitude and a desire to include."
Salford Clinical Commissioning Group, which organised the dementia awareness event, said: "We'll be speaking to the Lighthouse to establish the full details of what happened and why."
Listen to Premier's Anna Cookson speaking to Corin Pilling on Big Breakfast:
