She’s talking to another dude

This girl has been flirting with me for a while at work. Even my coworkers said she liked me. So i ask her out and she said yes. Then she texts me and said her mother wants her to stay quarantined so she can’t go out on a date. So i say okay, that’s fine. Then she said the guy she’s talking to wouldn’t like it if we went out. First of all, why would she said yes if she’s talking to someone, and why would she flirt with me a lot. Also which reason is it, her mom or the guy she’s talking to. i’m so confused