You need to go to the symantec web site and find the instructions for uninstalling your version. If you don't it won't be completely removed. I went to symantec.com and clicked on support and searched for remove norton antivirus. There were a lot of hits. You should narrow it down by typing your version in the search box. Here's the link: Removing Norton Antivirus.

Regarding things left in the registry that might well be true. However with the program removed the registry entries have nothing to control so become basically dormant. You say you have now installed an anti virus program. Is this a pure A/V or a combo A/V and anti malware? If only an A/V program you would be well advised to install an anti malware as well. The popular free program these days is Malwarebytes. If you are interested it can be downloaded from here. If you go elsewhere be sure you are downloading a legit version because the bad guys have spoofed this program. Also watch carefully if you install that you remove any check marks for toolbars or other stuff you may not want cluttering up your computer.

Have her first try running malwarebytes free and let it clean all it finds that may get it if it is not really conficker but something similar. Then there are specific sites set up with conficker cleaner tools to use. She can go register here and ask for help they will help her. LandzDown Forum Malwarebytes' Anti-Malware install this free program update it and run full scan let it clean what it finds it may ask for a reboot.

Many here feel that Superantispyware is superior to both Ad-Aware and Spybot Search and Destroy; perhaps it is. It is never harmful to have several programs for the spyware/malware stuff. I have these as well as Windows Defender. You are right about having only one anti-virus program, but in the spyware department, more is better. By the way, Avast is a great free anti-virus program, but don't run it along with McAfee.