Interesting Превед and NicholasG! Two genealogy websites; my heritage and geni) annotate Lili Dehn's birthplace as Revivka, Kremenchuts'kyi District, Poltavs'ka Oblast, Ukraine although they certainly could be incorrect.
The two Revivkas/Revovkas are on opposite sides of the Dnieper River:
1. Revivka, Cherkasy oblast, Ukraine. Location: 49° 3′ 21″ N, 32° 1′ 33″ E WEST Side
2. Revivka, Poltava oblast, Ukraine. Location: 49° 10′ 37″ N, 33° 44′ 21″ E EAST Side
I looked at both "Revivkas/Revovkas" on Google Maps and the Revivka/Revovka in Poltava/Poltavs'ka Oblast appears to be in closer proximity to the Dnieper River which Lily Dehn mentions in her book "The Real Tsaritsa" which is online on this site and an interesting read;
http://www.alexanderpalace.org/realtsaritsa/contents.html.
In addition, her son Alexander Leonid von Dehn wrote in a history of his family "The Horvaths Estates, my Mother's family on the Maternal side, have already been mentioned before, but, I will now describe the two Estates which I knew - my Great-Grandmother's estate, Revovka, near the small town Novo-Georgievsk, and my Grandmother's Estate, Beletskovka, where I spent many a happy summer in my childhood." This is also a really interesting and informative read;
http://www.genealogy.com/ftm/v/o/n/Holger-Von-dehn/FILE/0001page.htmlNovo-Georgievsk was a city in Ukraine that since 1961 was flooded by the Kremenchuk water reservoir; Wikipedia lists its Grid Coordinates as 49° 6′ 0″ N, 33° 7′ 0″ E. Plotting the grid coordinates for both Revivkas/Revovkas and the grid coordinates for the former city of Novo-Georgievsk (NG) on Google Maps, the Revivka/Revovka in Poltava also appears closer to the former city of NG.
However, as you mentioned the Horvaths, Dehn's maternal family, who owned Revovka, were registered in the provincial nobilities of the Kharkov, Kherson and Kursk gouvernements, not Poltava, would infer you are correct.
I love a good mystery.
Kind regards, JGP