Non-existent page in Custom menu???

On this page http://www.tuusulankennelkerho.fi/agility/
there’s a link on the right (ELINA MAUNO), which leads to a non-existent page http://www.tuusulankennelkerho.fi/agilitytoimikuntaelina-mauno/

I didn’t create the page (the customer did), so I don’t know what happened, but the problem is now, that I can’t delete the page/link since it doesn’t exist!
When I look at all the pages in Dashboard, it’s not there. Neither has it been selected in Custom menu to show on that page.
Interestingly enough when I deleted the old Custom menu and re-did it, the page “Elina Mauno” was a possibility to be put as a page where the Custom menu would show ??!

But I can’t find it anywhere to delete it!
The URL suggests it was created directly under the home page, but doesn’t help me to get rid of it.. help??