Can Vi Hot Headed use her ability more than once per turn?

Yes, Vi, Hotheaded can use her activated ability more than once per turn, provided you can pay the cost each time.

According to Rule 145.2, activated abilities can be executed at any time during your Main Phase while in an "Open State" (i.e., when there is no chain active and you have priority). Since there is no text on the card limiting the ability to "once per turn," you may activate it as many times as you have the energy and resources to pay the [2][C] cost.

As a reminder regarding the effect: Vi's ability doubles her current Might. Because this is an additive increase, if you activate it multiple times, each activation will increase her Might by her current total at the time that specific activation resolves (Rule 432.1). Each activation is a separate game action that happens one at a time, and your opponent will have the opportunity to react between each activation.