The 32-year-old right-back has been with Arsenal since the age of eight and has won nine league titles during her time at the club.
Coach Pedro Martinez Losa said: "We are very pleased that Alex has signed a new contract with us. Alex is a true leader who brings so much to our team.
"She shows professionalism on and off the pitch, providing a great role model for our younger players to look up to."

Putnam County Sheriff deputies believe the toddlers probably teamed up to work the pedals and steer the wheel before crashing it in a ditch.
The pair made it three miles (4.8km) down the road and successfully navigated multiple turns.
They were not hurt but officials are weighing charges against the mother.
They had taken their mother's 2005 Ford Focus after finding the keys in the floor mat while playing in the front yard.
Officials believe they were trying to reach their grandfather's farm but crashed five miles short in the town of Red House.
"Luckily, they didn't pass anybody because they would've probably had a wreck before then," said Putnam County Sheriff Steve Deweese.
Mr Deweese told WSAZ-TV that the sheriff's office is working with the county prosecutor and Child Protective Services to determine if the mother should be charged with any crime.

The disorder at HMP Erlestoke began on Saturday when two inmates escaped their cells and threatened staff.
No-one was hurt and those involved in the incident are being investigated by police, the Ministry of Justice said.
The Prison Officers' Association said the issues surrounded a lack of regime due to insufficient staffing levels.
A Ministry of Justice spokesman said "two separate incidents" involving three prisoners had been "successfully resolved" on Saturday.
He added the prison was now "running as normal" and said there had been "some minor structural damage".
He said: "We are absolutely clear that prisoners who behave in this way will be punished and can spend significantly longer behind bars."
The Prison Officers' Association (POA) said order was restored overnight on Saturday but said "both wings were destroyed and were now out of commission".
The POA spokesman added this was "another example of a failed benchmark process brought about by savage and unnecessary government cuts that has seen staffing levels decrease to an unsafe level".
Relatives of inmates also got in touch with the BBC saying prisoners were kept locked in their cells for three days, without hot food, hot water and no prison officers on some wings.
Conservative MP, for Devizes, Claire Perry said: "I was saddened to hear of the disturbances at Erlestoke Prison over the last few days.
"These incidents are wholly and utterly unacceptable, and I understand that these matters have been referred to the police to consider charges against the perpetrators."

She will talk about her life outside of politics, including television appearances on Strictly Come Dancing and Doctor Who.
Former Corries musician Ronnie Browne, along with authors Christopher Brookmyre and Lesley Riddoch, will also be festival guests.
The 12th annual event will be held from 1-6 September.

The Dow Jones was up 16.5 points to 18,533, the S&P 500 gained 5.15 points to 2,166.8, while the Nasdaq rose 26.1 to 5055.7 points.
Bank of America shares rose 3.3% despite a 19% drop in quarterly profits, which still beat expectations.
Shares of other US banks also rose, with Citigroup climbing 0.5% and Wells Fargo up 1.2%.
Technology stocks also rose on Monday.
Apple shares gained 1.1%, Google's parent company Alphabet rose 2.4% and Facebook was up 2.2%.
Streaming service Netflix climbed 0.4%, but plunged 16% in after-hours trading after missing subscriber targets in the second quarter following price rises.
Yahoo shares added 0.6% ahead of second quarter results.
England defender Alex Scott has signed a new contract with Arsenal Ladies.
[NEXT_CONCEPT]
Two brothers aged five and two stole their mother's car and wrecked it on a drive to their grandfather's house, say authorities in West Virginia.
[NEXT_CONCEPT]
A disturbance at a prison saw 130 inmates transferred to nearby jails after two wings were put "out of commission", a union has said.
[NEXT_CONCEPT]
Former Conservative politician Ann Widdecombe will headline this year's Nairn Book and Arts Festival.
[NEXT_CONCEPT]
(Close): US markets reached fresh intra-day records, lifted by technology and banking stocks.