A. She snuck out or she sneaked out?
B. The staff is in agreement or are in agreement?
For A you will probably need to be American to get it right.
For B, consider
I admit I was wrong. By replacing 'staff' with 'majority' I could still be wrong in the opposite direction!If the collective noun (staff) is acting as a single unit, use the singular verb: “The staff is very efficient.” If the collective noun is meant to highlight the actions of discrete individuals who are all doing different things, use the plural verb: “The staff are working on many projects for the holiday party.”