She may just not want you in her car b/c you may find something that she doesn't want you to see (re the carseat thing) -- that was my first thought -- not that she doesn't want you doing things for her.
Is she having an A that you know of? I would say she probably is.
No evidance of an A that I can find. I've searched high, low, far and wide. No changes in her schedule, no new undies, no new hair style or appearance, no new clothes. her schedule is pretty fixed, she is always where she says she is. Nothing on credit cards, cell phone or computer. No unexplained phone calls, does not keep her cell phone with her at all. no hang ups or unknown numbers coming into the house. No men work at her office. If she is I can find no evidence.