There is a 0% chance that you can recover any files from her PC without paying - the people that code these viruses do know their stuff and crypto.
Even if you pay, there is a chance that you won't get any decryption key. After all, customer service is not exactly what these guys are up to, as most of their customers don't want to deal with them in the future again.
You help her best by getting her a backup software, reformatting the PC and showing her how to do backups in the future. If you want to, you can try to pay the criminals instead, though I have my doubts that it'll work. Once Bitcoin ATMs become more widespread, these kinds of "data kidnapping" will also spread out, they already accept other digital payments like paysafecard for quite some time now.
I wouldn't say 0% because at one point everyone thought DES was unbreakable, and it got cracked. Then, the same thing with AES, and now that can be brute forced with related key impossible differential attack to reduce complexity to like 2^60. Complexity drops to 10^4 with side channel attacks. But yeah, right now if you open that .zip file in your e-mail, unless you can stop if before its too late... Well good luck not paying lol.