Only because most Ukrainians know and speak russian.
If she'd speak in ukrainian, russians wouldn't understand the shit.
Also it should be "Kruto", not "kracho".
Perhaps mangaka was trying to go with "классно" ("cool")? I mean, Japanese seem to have trouble telling "l" and "r" apart and Latin "H" looks like Cyrillic "Н" (only capitalized though). It's somewhat weird mangaka went from Cyrillic script to Translit (Russian in Latin script) mid-chapter, though.
Also, Oeconomist is kinda right there, you said "wouldn't understand
the shit" instead of "wouldn't understand shit" - that made a huge effect on the meaning of the phrase. I do agree that Ukrainian is hard for an average Russian, although knowing some regional Russian dialects helps a bit.