OK- you gave negative reponses on risk factor stuff, which greatly reduces the likelihood of viral infection.

The mushroom thing makes me think that it's soil-related. I'd definately re-pot, if only to get a look/smell of the rootzone. By the time that you're actually seeing mushrooms, you've got a whole sh*tload of mycelia in the media. May be a little wet, too...
See what ya see-and what ya smell.

You might want to start using a 'zyme product, if you're going to keep moms for a long time. Helps cleanup the detritus that builds up as part of normal growth.

So re-pot it, dry things out some, see what ya see...

I would keep it quarantined, though, and sterilize whatever tools you use, wash your hands,etc... If nothing else, you've got a plant with a compromised immune system- so even if this isn't a contagious disease, one of the inevitable secondaries might be.

Sorry I can't be more specific- but I do think that you have a chance. The symptoms sure do sound like mosaic- if you'd told me that the soil had previously been used for cucumbers, or that you had just had an aphid problem- then I would have told you to dispose of it quickly, and with extreme prejudice.