Parent Trying To Steal Investments Left To Their Child. Do We Need To Sue?

My niece’s grandparents setup an investment account in her name when she was born. She recently turned 18, her mother kicked her out after escalating abuse leading up to her 18th birthday.

My niece is now living with family members and we’re trying to get her setup for the future. One of the things we have to address is the investment account. I don’t know how much is in it but it’s in the 10s of thousands, I’m guessing about $20-50k.

The mother has called the police repeatedly on her child whenever they would argue, she soul use the police to threaten her own child. So needless to say, the mother will not give her child access to the account willingly. We’ve requested the transfer paperwork and intend to send it to her, in hopes she’ll just sign it and be done.

If she doesn’t (very likely) I guess we’ll have to sue, but i don’t even know where to start. What kind of lawyer would handle this type of lawsuit? Do I actually need a lawyer to file a lawsuit?

Any information would be appreciated!