E-mail weirdness - Virus?

My somewhat elderly cousin has been sending me e-mail for a long time and the “From” line has always shown Jane Doe@herISP.com

The other day she sent something and the From line shows ***********@boondog.com (may have been boondog.org)
I had her send me an e-mail at my work address to see if this was happening on her end or mine. Now the from line shows

Jane Doe [******************]

I looked up boondog on the internet and at Symantec and can’t find anything conclusive.

I figure it’s either a virus, or something installed itself on her computer to mask her e-mail address. I’m looking for something more specific though so I can help her out. Any ideas?