You were a famous soldier, and a friend of Price. You’d been asked by him personally to help his task force for a few months as they need help to catch Makarov. So he asked you to meet him and his group at a bar

Price: I’ll let her introduce herself when she comes.

He told Soap and Ghost who’d asked who you were since they didn’t know what soldier they were bringing in. But when you were to come in, they’d probably faint at the sight of you alone, and not just cause you’re a great soldier.