Makes me think Russian, maybe with a hint of French? Mostly it reminds me of some of the accents from the movie Anastasia.

Link that may or may not be blocked in your area. Listen to the blonde lady.
https://m.youtube.com/watch?v=w7S5TNCVZhY&t=0s&list=PLCD1lAsk9tIRWvGdhB-j9iYtSq9jU39rT&index=8

It's not really Russian; not at least not the pure Russian-English I seem hear here.

It reminds me most of Baldur's Gate's Jaheira, which according to this is Hungarian, but if you read the thread, you'll find it's not necessarily so (incidentally, from the thread it seems the OP there put Jaheira as Russian too, but was corrected later, so perhaps there is some Russianness there). I worked with a Hungarian girl before but can't remember he accent. I don't think it was exactly same as Ornella, though it could be because the girl I worked with spoke normally, and not like a cheesy teenage actress.

She does speak a lot like an aristobrat. :)

I did some sleuthing.

The actor's name is Sarah Sido (https://www.behindthevoiceactors.com/forums/printthread.php?t=18349)

She gave a great interview here: https://www.yesandyes.org/2016/04/true-story-im-professional-voice-artist.html

She's from Vermont.

So that's a Vermontian (Vermonter? Vermian? ??) doing a fantastical accent that I would say is attempting to be somewhere in the southeast European regions. But I'm no expert.

At least we can know it's definitely made up.

Yes, there are actually good similarities here, though I feel the blonde lady is a bit different, like this part:https://www.youtube.com/watch?v=w7S5TNCVZhY&t=37
"... love the Russian balet... " strikes me as different from Ornella.

Of course it could just be that the voice actresses in both cases purposely exaggerate it, so each sounds different (and different from what I hear in RL). Or it could be that Ornella's voice actress was just going for a generic East European without having anything specific in mind and without aiming to imitate a particular accent (and rightly so: after all this is a fantasy world, and for all we know this is what Bull Duchy residents in Ashan speak like).

After-refresh Edit: Thanks for the link, Tallima! (and as always it feels weird to see a voice actress's real looks).

The voice actress did add that 'R' sound (not quite rolling, not quite staccato) in Ornella's speech that seems (to me) to be stereotypical of an aristocrat vampire.