ML's relative has been contacting me quite a bit and has provided a number of useful reports & photographs. Possibly the most useful tip she shared with me has to do with Polish names. In Poland, some male nouns end in -ski, while the similar female nouns end in -ska. So a female with a dad's last name of Kaminski may change her last name to Kaminska. Keep this in mind when searching, as you'll likely want to search for both endings!
Also, keep in mind that up until 1918, Poland as we know it didn't really exist as a separate state, so ancestors may have reported that they were born in Russia, not Poland.