Wendy + Axe? Nah.
I don't see the sexual tension at all. i see her as manipulative + in control of every situation she is in - and it's awesome. Axe is a pathetic little baby, and she drives that bus exactly where she wants.
Everything Wendy does serves her best interest, and the beauty of it is that the men in her life have no idea. She lets Axe and Chuck both think they're in charge..they may wear the pants, but she picks them out, irons them and selects a matching tie.