As an employer, I'd consider it out of line to ask an employee to help in a crisis out of hours, unpaid. More so if they'd been effectively fired weeks before. As noted, the time to find other work isn't out of the goodness of her heart; it's the law in Belgium.
Employees giving their time for a panic, outside of their normal hours, is a privilege earned by employers through treating people right. Expecting those who've been shown the door to do so is twisted.
I've a Dell 3007WFP that I use with my 2011 MBP. It is positioned above the MBP with an unused fridge vegetable draw (perfect height, and locks it in place). Use the MBP keyboard, with just my text editor maximised on that screen, and everything else happening on the Dell.