What was Katherine Howard thinking?

So, at last post I was looking at The Tudors' take on Katherine Howard and how that show's presentation of Henry as a sexually vigorous and (due to casting, wardrobe and makeup decisions) youthfully good looking husband played into her affair with Thomas Culpepper.  After all, would someone who had a somewhat satisfactory husband (Katherine wouldn't be the type to have qualms about Henry's morality, and even if she did the script establishes Culpepper as also a bad person in the rape scene as discussed in he last post) consider an affair knowing that the very same Henry she was married to had caused the execution of her cousin Ann Boleyn on ostensible grounds of adultery? This definitely conflicts with the conventional narrative that she was getting little satisfaction from, and feeling no attraction toward, Henry and was thus, not being very smart, vulnerable to seduction.

Here's how The Tudors addresses the problem:  a scene opens with Culpepper frolicking abed with some happy lady...she doesn't look like Katherine, who can it be...OMG it's Lady Rochford!  Lady Rochford, as will be discussed down the road, was a pivotal character Ann Boleyn's downfall. It is historically correct as far as we know to believe she used her position as chief lady in waiting to facilitate the affair between Katherine and Culpepper.  Her motives there are variously explained, but we know that it didn't end well for her; she followed Katherine to the chopping block.

To get back to The Tudors, though, it seems as if TC keeps going on to Lady R about how he wants to get down with Katherine.  Lady R, who has already been established as finding voyeurism a turnon, offers to talk the Queen, who again isn't very smart and who is clearly already attracted to TC, into throwing caution to the winds. Kind of nuts, but entertaining.

Of the fictions that I've consumed so far, the one that delves deepest into the motives and circumstances surrounding the Howard/Culpepper affair and the role of Lady R is Phillipa Gregory's The Boleyn Inheritance. That book is told in three first person narrative voices:  Anne of Cleves, Katherine Howard, and Lady Rochford.  In Inheritance, Katherine's uncle, the extra-evil Thomas Howard, Third Duke of Norfolk, who engineered the Katherine/Henry match, becomes concerned when, months into the marriage, Katherine has not become pregnant.  His idea is to find a willing courtier whom Catherine likes, trick the two into having an affair, get a secret Howard into the line of succession, and arrange for the boyfriend to sleep with the fishes after he has done the impregnation.  He uses his henchman, Lady R, to get the plot going, and also of course to distance his own snakelike self from the goings on. Ms. Gregory says in the afterword that Norfolk and Rochford trying to engineer a pregnancy was her own invention rather than based on direct historical evidence.  Plausible?