Pros:
no commute, so never late
no commute, so no calls that she can't get in due to weather
already here, so she knows when kids are sick/misbehaving/tired and is prepared to deal with it
no commute, so she may be available in the case of an emergency (if she's home)
already here, and she sets her own schedule for household issues, so grocery runs and kids' laundry are when it's most convenient for her (no running out or worrying about when to do it)
already here, so no calls when she knows kids are sick, and she's more likely to work through an illness
if you are friendly, it's like having a sister or friend live with you

Cons:
already here, so she knows when parents argue over something (especially difficult when it's about her or kids)
there's always someone here
providing food
already here, and she sets her own schedule for household issues, so grocery runs and kids' laundry are when it's most convenient for her (convenient for her doesn't mean convenient for parents, but she does make sure not to inconvenience kids)
already here, so when she's sick, she may infect someone else
Burnout is more likely
Her PTO may be sitting around the living room, doing nothing, or she may be gone for a week. Either way, she doesn't have to do a thing. Resentment is possible.
if you aren't friendly, it feels like your house isn't your home

For what it's worth, I'm a live-in nanny. That's the list that my current and former families would give. My list is very different.

As to the rate for a live-in nanny, it varies. Most are $10-17/hour, but it depends on a huge number of factors.

pros - she lives with you

cons- she lives with you

Honestly - that's pretty much it. I'm 10 years into my live in and some days I love it, other days I hate it. It's super reliable and that's why I do it.

10-15 per hr.

What is the pay rate for a Live-In nanny in the Alexandria area? Pros and Cons of a live-in nanny?