I know this is so tricky.
I would definitely plan on giving yourself the full two weeks past due date. I don't blame you at all for not wanting her there before hand.
Besides, the final weeks before baby arrives is such an important time with your dh. A time to relax, go to the movies, do casual grocery shopping. Just momentous bonding time and alone time that will never come again. (In my opinion)
It is so different for everyone's family and I can only speak from my own experience with my mom. The help afterward was great. She really cleaned, cooked, and held our baby while I slept. She was also essential in helping me get over the "new mom" jitters. I literally didn't feel comfortable holding my baby at first, or attending to her. I just felt unprepared. Maybe this is different for you. I had never even seen a newborn before up close!
Two weeks is a long time, so perhaps you could request she only come the first week of September, which technically you could still be waiting for baby.
One final thought, it seems as if the weeks leading up to labor go really fast. I was just shy of 42 weeks with dd, and the final weeks of waiting were really calm and peaceful. (and so exciting)
I am hoping it will be the same for you