1. Yep, she works three days a week and is on call for a fourth, so occasionally she'll be working four (and will be paid the same regardless). Since she's a manager she's pretty much her own supervisor, so it's up to her discretion regarding extra shifts (which, for her, would mean filling in when an underling calls out). However, picking up shifts is primarily for participants to make up for having to take days off, etc. and while she can pick up a few to have a little extra cash now and then, it's not going to lift her out of her pay grade by any means.
2. Pay grade is associated with level, not the job. Unfortunately, that means she's probably not going to have money for vices for awhile since everyone here starts out in the same boat (aka poor). You can brush up on levels here
. You can earn additional levels by participating in monthly missions, and this one is always open to new participants
for an extra boost. Regarding currency, participants have an ID card that also functions as their house key and debit card, and credits are transferred there after shifts.