To me, when I meet a Slavic person with the name
Valentina, I always imagine it as having a "y".
Valentina simply looks Spanish to me. Now they don't say it on this site, but Valentyna is a known legitimate Russian spelling; it's the proper translation from the Cyrillic alphabet.
Thanks for the opinion though. I know if I met someone who didn't seem Slavic at all with the spelling Valentyna, I'd probably suspect it was a trendy spelling.