Tanisha Foster was in court Monday, trying to regain custody of her 10-year-old girl. Emani has been living with Nispey's sister, Samantha, since his death last March.

Nipsey's family was in court and squared off with Tanisha, whom they believe is not fit to care for Emani. The hearing was sealed ... but there's another date scheduled in July.

Tanisha's lawyer, Larry Lewellyn, tells TMZ he's working with Nipsey's family on a visitation schedule that will be in Emani's best interest.

As for Tanisha ... she left the courtroom crying and told us she's "pissed off."

We broke the story ... Samantha believes Emani's biological mother is unfit to care for the 10-year-old, and Samantha played a crucial role in helping raise her when Nipsey was alive. Samantha wrote in her petition that she wants to "ensure the continued stability for Emani and ensure that she will be able to maintain her current and ongoing relationship" with her fam.

Emani's mother, Tanisha, broke down crying in court last week, saying she hadn't seen her daughter in months. At the time, the judge gave them about 20 minutes alone together.

Still ... Nipsey's sister might have a strong case in asking for guardianship. Tanisha has a warrant out for her arrest right now, relating to an unsettled DUI case in 2017. She's also got a lengthy rap sheet filled with arrests dating back to 2006 and 2007.