Chinese Test: What does “我就知道” mean in Chinese?

Beginner Level 初级 (chūjí)
There will be a party tomorrow.
Míngtiān wǒ yào chuān nà tiáo wǒ zuì xǐhuan de qúnzi.
Linda: 明天 我 要 穿 那 条 我 最 喜欢 的 裙子。
Wǒ jiù zhīdào nǐ huì chuān nà tiáo qúnzi.
Mary: 我 就 知道 你 会 穿 那 条 裙子。
What is Mary trying to say?
A. She thinks that Linda should not wear that skirt.
B. She didn’t know that Linda would wear that skirt.
C. She figured that Linda would wear that skirt.

See answer at http://resources.echineselearning.com/minitestanswers/minitestanswers-chinese-739.html?ecl=ptEEEEEEpg080104