I'll try to answer to this as best as I can, since I'm new to this feminism thing there's bound to be stuff that I'll miss.
Well first of all it's very nice of her approving the use of image and Playboy too for not going after their rights. But I think it's far fetched to see her approval as a positive message. There are women out there contributing to the objectification of women too, for whatever reason they have. (One weird side of this is people think women are shielded from criticism of their own objectification, but it's a delicate matter to say the least. One has the right to objectify themselves so it's hard to say something without getting in the way of their right to self express.) There are more than one side to this issue; but it's not about her consent, it's about how it might be contributing to boys club image of tech.
It's easy to see that we have a problem of the lack of women in tech. I find this very depressing since they're able as much as men are and it looks wasteful to dismiss half the population. I think we're getting better each day, but it does not happen magically. People fight for it and will keep fighting until there's no discrimination based on sex. I accept that Lena image is one of the minor issues, but I still see this as one of the factors that drives women away. This boys club image of tech gives the implicit message that women are not wanted here.
I know there's no nudity in the image and one needs to research to find its origins in Playboy so it seems unlikely to come across it. But the real reason here is if we're willing to combat sexism, it will give women comfort that we're willing to change tradition to be more welcoming. I believe actions speak louder than words, and if the reason to keep the tradition is not all that important, we should do it.
(I also don't think it's fair to compare it to an image of a naked guy, since it's unlikely to drive boys away from tech. It's not just naked guy vs. naked girl, the context and the message makes a world of difference.)