Disclaimer: I work in this area.
The first thing is to figure out what her expectations are. Do they need to be able to be back up within 15-30 minutes after a catastrophic server failure? Are they willing to pay a premium for immediate responses and a Datto backup system that can spin up the 15-minute backup as a VM locally or in the cloud? Or do they want to pay $10/month for remote monitoring, patch management, managed AV and remote support? Because if they want that, she's going to be disappointed with what she finds.
The simple answer is to network with other small businesses, find out who's happy and who they're using. If she's at a company in a specific vertical market it makes sense to talk to vendors who are focused on that market, particularly if it's one with special needs (e.g. healthcare, accounting, finance, construction, etc.).
In terms of costs it'll vary some by area but it's not going to be cheap - if you want to avoid hourly charges, you're probably looking at $75/month per workstation and 3-4 times that for each server. One number I've seen is that on the vendor side for all-inclusive plans expect to have 20-30 minutes of technician time per machine per month, and figure if you have skilled techs they're making a minimum of $25/hour (or they're going elsewhere in today's market). With benefits, overhead, etc. figure there's $20-30/month of technician per workstation, plus another $5-15 of software licensing for RMM, AV, backup, another $1-5 for ticketing and documentation software, plus business expenses divided across the number of systems managed, and finally some level of profit margin. You can get all of that cheaper, but if it's too much cheaper then corners are getting cut somewhere. $30-40/month is not an unreasonable amount for just the monitoring, patch management, AV and remote support, but at that level expect to pay hourly for any time onsite - and backup's probably billed separately.
If they're paying $15-20/month they should be expecting to get charged for every call or visit because that's barely going to cover the cost of licensing plus basic business expenses, and likely corners are being cut in some areas.
Finally, do they have perpetual license versions of Office or are they on Office365? If it's O365 are they getting it through the IT vendor? If so that vendor's probably paying $12-15/month or more for each license depending on exactly what they have, or if they're paying it separately the vendor's maybe getting as much as 6-8% on Microsoft's CSP program - not exactly a way to get rich or cover the cost of any support being provided.