Being an Antag with Valeria is ridiculously hard, She so damn slow and her ability doesn't compensate for that at all, leaving her unable to make an
effective tactical retreat.
Her gun itself is a pea shooter, and once you activate her ability, (which is easy to spot) every one splits from its direction and that offensive opportunity goes out the window. Which leaves her with only melee as an option.
The only time she becomes remotely effective as an Antag is if you somehow manage to funnel the group in one location which is rare and difficult to maintain a lockdown.
In short, Valeria is meant to be played as a Raider not an Antagonist. Which is a real pity because she looks so sinister and cool with her Vlad the Impaler vibe.