I think they forgot it in the kitchen, and she didn't realize.
And then when she went to get the bill for you, she realized that you hadn't gotten it, so she didn't charge you for it.
when you said, "I didn't get my maki" (did you gesture to the bill?) she 'heard' "you didn't charge me for it."
And she answered, "Yes, we didn't make it for you." Meaning, "we already knew that you hadn't gotten it, because we didn't make it, so I'm not charging you."