As one if the requirements when doing a review on a provider that has never been reviewed, you must show their web site URL.  
I have seen two providers that were not reviewed here before. One has a listing on P411. The other only has a listing on another review site
 Because reviews are not part if the P411 experience, I think I remember that it is fine to indicate that as an I do source for a provider. I also think I remember that another review site may NOT  be shown as a URL for a provider.
It's been a few years, of course, since my last review and the memory grows hazy.

You can NOT any competitor's site.

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I'm not positive but I think that may be acceptable.  

Also, if you haven't already done so, try googling her contact info.  Sometimes an old ad on a site like STG might turn up and, even if she doesn't currently advertise there, this might also be allowed.  

HTH!