I don't get the whole "struggling through infertility" part.
Yes she went through IVF but she made it perfectly clear for the duration that this was never her 'problem'.
She wanted a man to provide and knew having a baby would achieve that. It seems to me that, in her eyes, she unfortunately picked someone who couldn't give her that and she was determined to do what she could to get what she wanted (an easy ride). I think of she'd have lost the weight prior to marriage or before IVF her affairs would have started right from the off. She seems like the type who'd get knocked up, claim it was a miracle and happily let Richie pay for their life.