Her Personality:

Marie is seemingly quieter and not as excitable as her cousin, and usually only gives a half-smile, if at all. She can be a little sarcastic from time to time, and slightly prone to complaining, but is usually in a mild mood. Overall, her disposition is laid-back and friendly/grumpy. She is also an expert at doing impressions, as mentioned by Agent 1.

She dislikes overly-thrilling activities, and can even be somewhat lazy. She also doesn't seem to be a big fan of tomatoes.

When anticipating an announcement (for example, the theme of a Splatfest, or the contents of an update), she often repeats herself in excitement. (Ex. "What is it? What is it?!")

She mentions several times on Inkopolis News that her preferred weapon class is the Charger. Given the existence of the Hero Charger Replica and her role as Agent 2, it is possible that Marie used a Charger in Octo Valley.

Try to Image What she Might sound like from the Actual Games.

Ref: https://www.youtube.com/watch?v=tiNgr1mQ1qc