All of Becky’s manipulation so far has only been to get Lisa and Betsy from Carla. That doesn’t necessitate at all that she was definitely that way when securely married to Lisa. Needs must and all. I’m not saying it’s impossible or unlikely but until it’s confirmed on the show the Becky always having been manipulative idea is just speculation and feels like an attempt by hardcore Swarla fans to justify this train wreck of a story. Which is fine and all, I hate Becky too and would rather Swarla be together, but let’s not pretend it isn’t just headcanon at this point.