A grand jury report said the longtime legislator micromanaged every detail of the party - choosing everything from napkins to ice sculptures and playlists. When one staff member questioned the legality of planning the parties in the office, according to the report, the senator belittled him, cut his salary, and fired him.
Washington has vowed to fight the charges, which her lawyer called "thin and specious."
Birthday parties doubling as political fund-raisers are typical in Philadelphia, political experts say. Last year, Washington netted nearly $12,000 in the weeks around the party, about 60 percent of her fund-raising total for the year, the grand jury found.
The problem with Washington's bashes, the state Attorney General's Office contends, was her use of staff time and public resources in planning the event, which may have cost taxpayers more than $100,000 from 2005 to 2013.
Last week, Washington, 68, was arraigned on two felony counts of theft of services and conflict of interest. If convicted, she could face up to 12 years in prison.
Washington, a Democrat who represents Northwest Philadelphia and southeastern Montgomery County, has earned praise for her candor and advocacy as a survivor of domestic violence. Otherwise, she has maintained a relatively low profile over her 20 years in the legislature, which included six terms in the House.
She was absent for nearly a third of the 2012 and 2013 sessions, missing key votes on voter ID, Medicare expansion, and other controversial issues, an Inquirer review of voting records showed.
But Washington has rarely faced a real election challenge, and garnered at least 70 percent of the vote in each contest in the last decade.
The charges against her highlight the pressure associated with political fund-raising, particularly for local legislators, who often rely on one big affair per year.
"If somebody's going to the well every quarter, people might view it as just another event," said T.J. Rooney, a political consultant and former state chairman of the Democratic Party. "If it's known that that's their primary event every year to raise money, it's a little different; people are more open to it."
A number of Philadelphia politicians - including Councilmen Curtis Jones Jr., David Oh, and Kenyatta Johnson, and State Rep. Jordan Harris - have held fund-raising birthday parties in recent years. According to invitations obtained by The Inquirer, ticket prices range from $50 to $5,000.
State Sen. Anthony Hardy Williams, the Democratic whip, is scheduled to have such a party on Saturday. The event - expected to draw 400 to 500 guests at the Hilton Center City - is considered one of the hottest tickets in town.
Williams, in an interview, said birthdays "are an easy thing around which to raise money," adding, "It's just a celebratory period in your life, and people want to celebrate around you."
Williams said he has no role in planning his party, which is done by a volunteer with his campaign. "My job," he said, "is to show up, say hello, be happy."
Washington took the opposite approach, prosecutors allege.
According to the grand jury presentment, released Wednesday, several Senate staffers testified that Washington "made all decisions regarding the event."
She would repeatedly review the invitation list and "say yes or no to the individual, and decided what dollar amount would be on that individual's invitation," the report says.
Prosecutors say she directed legislative staff to organize vendors, design invitations, and log campaign contributions from her Senate offices in Philadelphia and Montgomery County. Invitations - as many as 1,500 - were printed on Senate computers and until 2010 were sent with Senate postage, the report says.
Washington's lawyer, Henry Hockeimer, said the grand jury report blows the event out of proportion.
"This birthday party was essentially an informal gathering, almost like a cookout," Hockeimer said Friday. "Certainly not the way it was portrayed, as some kind of gala."
According to the grand jury's report, fund-raising totals each year ranged from $10,000 to $29,000 in the weeks surrounding her July 28 birthday.
That pales in comparison to what higher-ranking politicians can net. In March 2012, for example, when Williams had his birthday party, he raised more than $44,000, according to campaign-finance records - about four times what Washington raised around the time of her party that year.
Larry Otter, a lawyer and former Democratic committeeman, said officials with prestigious titles tend to have the most successful parties.
"If you become chairman of an important committee or subcommittee," he said, "a lot of people want to know your name, shake your hand, blow out the candles on your birthday."
Inquirer staff writers Troy Graham and Bob Warner contributed to this article.