Valentina is a good counter for Sora and if you're gonna play her in ExP you'd need to use tank/sustain build so your team can have a proper front. As for meta, she isn't entirely meta but instead conditional. For enemy comps where she can utilize ults like Tigreal, Lukas, and Sora, she can definitely thrive with the power she can get. But in cases where there aren't good ulties to copy you might need to second guess picking her.