Jennifer Laxson is the type of person Philadelphia wants to attract.

A young professional and entrepreneur, she moved here by choice, bought a home in a growing neighborhood, and recently started a business - a line of dresses called J. Laxxy that she sells online from her basement headquarters.

But just three years after moving to the city, she has become another archetypal Philadelphian: the frustrated taxpayer who wonders whether she wouldn't be better off moving to the suburbs.

It's hard to blame her, considering the tax bill she received in 2011 for her Graduate Hospital house. It was more than $10,000; the average residential bill in the city is about $1,350.

"Obviously, I went into kind of a panic mode," Laxson said. "I was dumbfounded by the whole thing."

While the Nutter administration moves to reform a property-tax system rife with historic inequities, Laxson has emerged as a harbinger for a new class of victims: the owners of tax-abated properties.

Laxson, 33, bought her 1,100-square-foot home in 2009, knowing that the house was in the final years of a 10-year tax abatement.

"I guess I didn't really understand the tax implications," she says.

After living in New York and Los Angeles, she was thrilled to get a house for $285,000 - a bargain compared with those other cities.

The assessed market value was $350,000, but that hardly mattered as long as she was paying only $453 in taxes. She knew her bill would go up in 2011, but she never imagined it would rise to $10,563.

For that price, Laxson said, "I should be living in a half-million-dollar house in the suburbs."

The well-documented problem is that many houses in the city are wildly underassessed - as much as three to 31/2 times below market value, according to recent Council testimony.

But homes that were built or had major renovations under the 10-year abatement program were assessed near their true values (Laxson's was actually overvalued).

When the abatements expire, owners of those properties can end up paying drastically higher bills than their neighbors.

Sympathy can run low for abatement beneficiaries, who generally are well-to-do and enjoy 10 years of tax breaks - they pay taxes on their land but not on their new home or significant renovations - and had 10 years to prepare for the abatement to expire.

Kevin Gillen, vice president of Econsult and an expert on the city's real estate, said anyone shocked by a post-abatement bill was being "willfully ignorant."

Nonetheless, he said, "if there's enough of them that are willfully ignorant but upset, then the city has a problem."

But what about folks like Laxson, who only enjoyed two years of the abatement? And how could homeowners like her sell their properties with such a hefty tax bill attached?

It's an issue that hasn't gotten much attention because relatively few abatements have expired. The first ended in 2009.

Introduced in 1997 to spur development in the struggling city, the abatement program is widely credited with jump-starting Center City development, but also decried by many property owners who have felt the brunt of two consecutive years of property-tax increases, with a third on the horizon.

The Board of Revision of Taxes, which hears appeals on assessments, had 2,000 cases filed for the last tax year, but few involved formerly abated properties.

"We've had some," said Alan Silberstein, chair of the BRT. "But if it's 10 percent of the cases, it's a lot."

Nutter's property-tax reform effort - the Actual Value Initiative (AVI) - was designed to solve the system's long-standing maladies. But it would solve the Laxson abatement issue as well.

Estimates of the tax rate under AVI, as discussed in Council, range from 1.25 percent to 1.7 percent of market value.

Assuming that Laxson's home retains a market value of $285,000, her potential bill under those rates could be between $3,562 and $4,845. That's without taking into account homestead exemptions or any other potential relief measures under consideration.

In the meantime, Laxson has to deal with the fallout from her 2011 bill. Her bank paid the $10,000 and, figuring that she would owe the same this year, more than doubled her monthly mortgage and escrow payments. The bank gave her a grace period to appeal, but her time runs out in June.

Laxson appealed her case to the BRT, which lowered her assessment to $140,000 - not quite in line with reality but more representative of other flawed assessments.

Silberstein said the board takes into account how inaccurate assessments are citywide, figuring that all properties - including commercial and industrial - are undervalued by half.

He didn't remember Laxson's case specifically, but figured that the board must have arrived at $140,000 by halving her 2009 sale price.

Laxson also benefited from the city's trouble with the State Tax Equalization Board, which checks the city's math on property tax. For decades, the city was supposed to tax at 32 percent of the market value, meaning that a house worth $100,000 would be taxed on $32,000.

In July, STEB said the city was taxing at more like 18.1 percent. That opened the door for appeals from homeowners saying, for example, that a $100,000 house should be taxed only on $18,100.

The BRT not only lowered Laxson's market value to $140,000, but applied the 18.1 percent. The city's lawyer told Laxson that the city would accept the $140,000, but only if she paid at the 32 percent, making her bill about $4,225.

Laxson refused the city's offer, and both sides have filed appeals. They don't yet have a court date.

"The first thing you want to pull your hair out about is, we're still playing 'let's make a deal,' " said Brett Mandel, an activist who has sued the city over its property-tax system. "We shouldn't have the BRT making up a ghost value to help someone. We shouldn't have the city saying, 'If you don't accept this number we're going to sue you.' "

Laxson said the attraction of the city's affordability has been withered by her tax saga.

"Maybe," she said, "it's not cheaper than L.A. and New York anymore."