Removing a virus without an anivirus?

I mean a lot would depend on the type of virus in question, but generally deleting infected files would likely be the way to go. Some viruses can infect other files which could make this slightly tricky. Looking around Task Manager for any suspicious processes and following their source could help. Chance are that if she is unaware of the free options she would likely be unaware of how to do this too.

Depending on the operating system, there are some in-built features that help with this (they might not really do that, sometimes but it's still worth a try). In Win10 there's Windows Defender for an example. While paid versions of software might provide better results, the free options are not insufficient in most cases.

Malwarebytes and any other free anti-virus (just google 'free anti-virus list') would most likely solve the issue, but again depending on the virus in question they might not. Worst case scenario your friend could always try re-installing the operating system which most likely would fix it. Again, there's many unknowns as to whatever she is using and what sort of virus it is.

If its a rootkit, have you tried an incinerator ?

An Anime List website probably isn't the best place to find this answer. You should try other websites.

just use malwarebytes free

You can just use a free antivirus like malwarebytes, avast etc. Windows defender can do the job pretty easily as long as its not ransomware. Just try to find the file thats suspiscious and get wdefender to put it in the sandbox and delete it.
Youd need to give more info if its another kind of virus

malwarebytes comes with a month of free trial, hope that solves the issue

malwarebytes is free, and works for me.

reset your pc