SNOHOMISH COUNTY, Wash. -- A 92-year-old woman just got a stunning tax bill.

The value of her land had jumped by hundreds of thousands of dollars. But the tax assessor insists she had actually been getting a tax break for years.

Barbara Tredway and her mother Bertha spend a lot of time enjoying the family property. Bertha has lived at the same place for 50 years.

"When you're older and you can't really get around too much. It's nice to see the season pass," Barbara said.

While time stands still at their Bothell home, the value of the property has not.

The Snohomish County assessor just upped the value of their 1.5-acre property from $40,000 to more than $830,000.

"I looked at it again and I thought 'What in the world is this?' This is huge," Barbara said.

The county admits for years, assessors overlooked and undervalued Bertha's land; its new value is correct.

"There is no limit on how much your value can increase," said assessor Cindy Portman.

Now Bertha is on the hook for a huge tax bill.

"It's almost $7,000 for the year and it's about half of her income," said Barbara.

Bertha already gets a senior citizen exemption on the lot her house sits on. The tax bill is for the rest of her land. If the family can't pay...they might have to give it up to developers.

"In this case it was probably a mistake in the taxpayer's advantage in that they haven't been paying higher taxes that they probably should have for the past few years," Portman said.

But the county made the mistake, not Bertha.

"If they could just say 'OK, it's going to go up and we'll give you 3 years of a graduated increase and then that's going to be the tax' just for us to get used to it," Barbara said.

"Absolutely not," Portman said. "We are required by state law to assess property at fair market value."

Bertha doesn't like to think about new homes in her backyard.

"I wouldn't like it," she said.

"It means a lot to her. It's her home," said Barbara.

Bertha and her family are trying to qualify for an open space program that would off the tax bill if they promised not to develop their land.