I keep getting emails spoofed to a relative's email address? How can I get this to stop?

Tell your relative to stop visiting questionable websites; porm.

They are probably now an Email Zombie. People will take over a machine and use it as a Proxy to send out spam so it appears from a user you know. It is even easier to do this with something like Google+, which is why I never log in to that service unless I have to, then log out again.

And, yes, never click on a link in an email, ever. Unless you know for certain it is legitimate. I won't even click on a link my parents send me to a youtube video. Instead, I search for the video myself.

What you can do to determine if the link is OK is to copy the link and paste it into a notepad document. Dodgy url addresses always look dodgy. Usually something is added before or after the corporate name that they are trying to fool you into thinking they are.

You can't stop it. The most you can do is flag it as spam.

Most likely what happened was your relative's email got compromised and so they're now using her address to spam her contact lists in hopes you'll just open it up. The only way it'll stop is if they stop.

The 100% guaranteed way to find out if an email is being spoofed is to look into the header to see if the right SMTP servers are sending the mail.

Their password has been changed and, since they're in my address book, an official email from them shows up as in their name - not their address. This show the latter, so I'm pretty certain it's been spoofed.

None of that matters. Once an email has been compromised, it's been compromised. They have the user's name, mail address, and contacts list. They'll send you spam until either they decide to stop or someone (ISP, gov't) forces them to stop. There's nothing you can do to stop it and the best you can do is flag it as spam. If your email's spam system is good enough, it'll realize the reason you marked it as spam is because of a spoofed from address.

Spoofing a from address is incredibly trivial and done all the time for both legitimate and illegitimate reasons.