But it is frustrating to be second-guessed as a mother.
Very true! I had the same feeling with my first child. And it was hard when it's your own mother/mil questioning every parenting decision you made.
I have an Indonesian helper, and she's behaving quite similar to your helper, Gracey, with my second baby. Overprotective of the baby, swaddling her very tightly, always trying to put her to nap even when I told her not to overdo it, etc. Talking only got me so far, so (since I'm a SAHM) I would simply hold the baby when the helper's trying to put her to sleep (and the baby's not sleepy), and tell her to go about doing whatever she needs to do (cooking, cleaning etc). We are getting ready to sleep train the baby in a month's time, which will involve a lot of crying and not picking up. I'll be expecting a lot of resistance, from both helper and baby!
To the OP, sometimes being firm is the only way to do it, be it with helpers or family. A good helper must understand that she is an employee, and while she may have her own ways of raising children, she must respect and put your ways before hers. Unless it's clearly putting the child in harm's way, she should understand that there are just different ways of parenting. If you don't get this sense from her, perhaps she is not the best caregiver for your child.