IANAL, but if she traded a picosecond after tweeting: no. If she has zillions of followers and traded a year later: yes, because ’the public’ could be aware of the content of the tweet. A judge will have to decide on in-betweens. When doing that they likely will take into account how open Twitter/X is.

> If I saw the tweet and trade is that legal?

Again, IANAL, but I would think so, if she has ‘enough’ followers.