Have heard of this before, is it something to do with the hormones which are out of sinc due to op. Believe it passes , could you remove the cushion pro temp.
Although the majority of hormones are produced by the ovaries which are taken away when a bitch is spayed, some hormones are produced in the adrenal glands, If bitches start mounting people, and/or other dogs, it is usually a dominance issue.
Its often a 'learned' behaviour and not a hormonal one so spaying would not have any effect. She is dominating it as she would a younger female or puppy. Try giving her something to distract her, such as a chew or a bone, but I would not worry about it.
lol my female labrador did this for a few months, to her finding nemo teddy, we took it away and it stopped....hasnt done it since, that was approx 2 months after the op