Cristina seems to be an acquaintance of Lincoln, and attends the same school and class as him. She has not had any speaking roles yet. Lincoln has, or at least had, a crush on her, though the feeling does not appear to be mutual. How Lincoln got a crush on her is not known, although he mentions "the way [she] looks at [him] in the lunch line".
She first appears in "Making the Case", when Lincoln wanted to apologize to his sisters for posting his video of them displaying their most embarrassing secrets and moments, by making an even more embarrassing video about himself, one of the things he did was put a photo of Cristina over one of Lucy's dolls, and pretended that they were a couple, speaking romantically to it, and attempting to kiss it. When Cristina saw this, she was rather uncomfortable about it, and as Lincoln explains, switched classes, presumably to avoid making any further contact with him. It is unknown if Lincoln still likes her after that.
In "The Green House", she makes a cameo at the beginning of the episode fawning over the picture of the polar bear alongside her classmates.
Cristina later makes a cameo in "For Bros About to Rock", where Luna notices her, and thinks she's perfect for Lincoln, apparently not recognizing her from Lincoln's embarrassing video in "Making the Case". Lincoln doesn't make any comments about it (only getting angry at Luna for her meddling), and Cristina just disappears from the scene later.
Since more recent episodes show Lincoln reciprocating Ronnie Anne's feelings for him, it's possible that he may have gotten over his crush on Cristina.
Cristina wears a navy blue blouse with a matching colored skirt, with blue shoes, white socks, and an orange headband. She has very curly ginger hair, and wears orange earrings.