I think generally it is a case of what type of hammer is appropriate. You need a pin hammer to set a picture hook, you need a sledgehammer to smash through a wall.
If it's a noob and fall for stuff like this, provide that person with adequate defense. If they're savvy and will stop to think twice about visiting 214124.norton.web.uk.scamlol and then entering all their stuff and talking to someone asking for £400 to unhack their IP connected CD rom drive then MSE is fine.
I don't blame you for recommending Norton. It's ironic however that the brand in this case made them blind to a scammers that exploit the idea, "If it says Norton on it then I'm safe, shut up and take my money".
Obviously glad your sister called you
and it's fortunate the scammer asked for such a ridiculous amount of money. It's kind of insulting they thought your sister was that stupid though (or they wouldn't have proceeded), and good therefore that she called you.
It's scary because this can easily lead to things like encrypted system files, disk deletion of sentimental or valuable things or identify theft and credit/debit card fraud.
I would full format the disk and reinstall Windows from a disk however. I only say that because for me it doesn't seem to be a pain to do so, doing this stuff for family and friends etc is a right pain in the arse because they just never learn. You've probably spent hours faffing around with it but you can't fix your general computer user's vulnerability to psychological exploits. Sorting it out while knowing it'll probably happen again is the dread of working with computers.
(case in point, I have an ex boss who still asks me for passwords I provided in database when I left
4 strawberry floating years ago because they can't keep their gooseberry fool together and every single time they ask me to email it to them they create a security risk)
It's a shame it wasn't flagged up by Google or Mozilla yet.
Were they using Internet Explorer?