Question: Why does Freddy use Alice to gain access to new victims?
Answer: He'd killed her friends in the previous movie, remember? When he came back she'd had time to recover and make new friends.
That was Kristen, not Alice. Alice gives the answer to this question herself, while talking to Dan in the diner. She says that Kristen was the last of the children of the people who killed Freddy, and "maybe Freddy can't get to the new kids unless there's someone to bring them to him."
Answer: As Kristin was being burned to death in the boiler, she passed her ability to pull other people into her dreams to Alice. This enabled Freddy to get new victims.