It's mostly to tease Ian. In the cuck/resolved to cheat branches where Lena chooses to go full way for the "other side" sunscreen and the photo follow-up she's watching Ian's reaction.More like a tool to hurt Cindy.
Unless the next part speedruns Lenas and Wades relationship akin to Ian developing feelings towards Louise over some shitty text messages, she is only seducing him for a power trip and to get leverage over Cindy.
But yeah, Wade being Cindy's boyfriend is probably contributing to this, especially if Lena heard rumors about Ian fucking Cindy.