Debbie is a woman whom Oliver dated.
Debbie works in Ben's office. She and Oliver met and chatted for a few minutes and he liked her. When he saw her again at the diner while he was eating with Ben, he asked Ben to put in a good word for him with Debbie. Ben initially refused because of the way that Oliver treats women, but when Oliver caught him in the lie that Debbie already had a boyfriend, Ben agreed to help him get with Debbie after making him promise not to dump her once he'd had sex with her.
Oliver and Debbie had a night in together and at the end of it, they slept together. However, Oliver realized that she mimics sound effects for everything, a habit he found very annoying. He stuck with her only because of the promise he'd made to Ben. When he found out that Ben was having his own shallow relationship with Alana, he dumped Debbie, finally able to do so without feeling guilty.
She briefly dated Oliver Barnes. The relationship went south when her habit of mimicking sound effects in conversation annoyed him.
She works in Ben's building as a fellow therapist.