Can a person in CA with a green card get in trouble if they're being sued in Small Claims Court and have a restraining order against them?

Do you mean in more trouble than they are already in. What is the restraining order for, has it been proven, has the law suit is civil and has no bearing on the immigation

Can a person in CA with a green card get in trouble if they're being sued in Small Claims Court and have a restraining order against them?

The fact that you are being sued in small claims court will not jeopardize your green card.

If a restraining order against you has been issued by a court, as long as you obey the terms of the order you should be all right.