Remote Drive under Locations

Remote Disc is an Apple Service that allows you to use a SuperDrive (CD/DVD drive) from another Mac. It is very limited in what you can use on the remote drive, designed primarily to install software on the MacBook Airs when they were first released and didn't have their own CD/DVD drive. You should be able to drag it out of the SideBar and it will go away (if you don't need to access another Mac's SuperDrive).

Biggest thing you need to worry about is account passwords. Make sure you go online and change all of her accounts.

They couldn't really get to them without her giving them the user account password, but she may not remember giving it to them. Make sure you use different passwords for each online account.

Anyway after looking at her Mac I noticed that there was a Remote Drive under Locations in the side bar

Those are other devices on the network advertising their services. It could be a memory card in a printer.

Does it say "Remote Drive" or "Remote Disc?"

However I did notice that her Firewall was not on (she had purchased a new iMac after replacing an old one last year so I am curious to know whether new Mac's come with the Firewall turned on or off as a default as I thought that it was already on when you purchase a new Mac?)

If she is behind a Network Address Translation (NAT) router, then she already has a "firewall" that works better than the application firewall in the Mac. If you are behind a NAT router, there is nothing on the internet that can see your Mac unless you poke a hole in it with screen sharing or things like TeamViewer. They will trick people into installing things like TeamViewer to gain access.

I had to get help from Microsoft for a licensing problem with Office. The support person was absolutely baffled that I wouldn't let her connect into my Mac remotely. It may make it easier for them and the customer, but it also creates the impression that letting someone remote into your computer is Ok under any circumstances.

A Firewall is not a security device. It is a network management tool. It isolates devices and users from other devices and users.

The only utility of the built-in firewall is if you have a laptop which you connect to public networks and have a lot of sharing services enabled. It is then easier to enable the firewall to essentially turn off all of the sharing services at once instead of doing it one-by-one.

If there are no Sharing services enabled, there is no need for the firewall.

Regardless, they're just going to intercept your wifi connection which is simpler to do than hack your Mac.