The rapper met with Guillen's sisters at Taqueria del Sol in southeast Houston, which has become home to a notable Guillen mural.
He surprised the family with a check for $30,000.
He told Eyewitness News he's been raising money for the family by selling merchandise.
"Vanessa is a Houstonian," said the activist. "I'm at a point in my life where we have to protect our women. We have to protect us all, but we really have to protect our women. It's a disappointment when people cry out for help and we don't take it as serious."
A memorial service for Guillen will be held this Friday at Chavez High School at 8 p.m. The event is open to the public.
According to the family's attorney, Natalie Khawam, the Guillen family will host a private funeral on Saturday, Aug. 15, and Vanessa will be laid to rest at Forest Park Lawndale Funeral Home.
During a meeting between Vanessa's family members and President Donald Trump at the White House last month, the president told them that they have his support and that he will personally help with funeral expenses.
"If you need help with the funeral financially, I will help," the president told the family in the Oval Office at the time.
READ MORE: 'I will help': Pres. Trump pledges to pay for Vanessa Guillen's funeral
Ahead of the meeting with the president, several dozen demonstrators joined the family at a rally calling for Fort Hood officials to be held accountable for Vanessa's death and for better investigations of harassment in the military.
"Fort Hood is supposed to be held accountable. Leadership has to be held accountable," said Lupe, Guillen's sister, while speaking to a crowd outside the U.S. Capitol.
Supporters marched from the rally at the U.S. Capitol to the White House.
WATCH: Vanessa Guillen's family leads rally in Washington
"We are here to demand justice for Vanessa," said Khawam.
The proposed, #IAmVanessaGuillen bill, would let service members file sexual assault and harassment claims to a third party, rather than their chain of command.
SEE RELATED STORY: Fort Hood soldier Vanessa Guillen may have been harassed, Army officials said
The bill comes after hundreds of Fort Hood service members have come forward with their experience on the base.
SEE RELATED STORY: President Trump shares sentiments on Vanessa Guillen's death