Ann Parry, 73, left her Mercedes A-Class at St Mary's Church in Shenley Church End just before 9am on Sunday morning.
Then the 35 foot ash tree came crashing down, slamming into the driver's side of the car.
Ann's daughter Jill Mohan told the Citizen that if her mother had been in the car, she would have faced certain death.
She said: "It could have killed her. It was a huge tree, over 30ft tall, and it landed straight on the car.
"She had been in it just minutes before so it was really quite lucky.
"She was still very shocked by it all, though, and the car is a write-off."
Church warden Alison Baird echoed those sentiments, and said it could also have been tragic if the tree had toppled moments later.
She said: "It happened before service and most people hadn't arrived yet. There would have been more people in the car park closer to service and it was lucky no-one was in the car.
"In fact someone had parked there already and decided to move, which was a stroke of luck!"
According to Jill, neighbours around the church have been complaining to Milton Keynes Council about the condition of trees at the church.
Most are well over 100 years old and she said they had been concerned about the one which fell in particular.
"All the residents have been complaining about that tree for over a year," she said.
"A man who saw it happen said the tree just fell completely on its own, there was no wind at all, not a sound.
"And the tree surgeon who came told us the tree was dead."
A council spokesman said: "We do not have a record of any complaints regarding a potentially dangerous tree in the wooded area on top of Dudley Hill in Shenley Church End.
"The tree was due for removal as it had been identified in our annual tree survey as being in poor condition.
"Unfortunately we were unaware of the presence of honey fungus within the base of the tree, which is very difficult to identify through standard monitoring procedures.
"This fungus decaying into the roots led to the tree's unexpected failure.
"We take the health and safety of our residents very seriously and now that this problem has been highlighted, we are examining the remaining trees in this area."
