As a vampire, Yuloli naturally possessed the weaknesses common to her race.
These included reduced activity during the day, a slight decrease in ability values under sunlight due to racial penalties, and lower resistance to damage from fire and holy attacks.
In addition, weapons made of silver or mithril could still harm Yuloli's body. Although such injuries were not fatal, unlike Shalltear Bloodfallen, who possessed low-level weapon damage resistance skills, Yuloli could not completely ignore these metal weapons, and they posed more or less of a threat to her.
Therefore, Yuloli didn't particularly like to be near silver objects. Although not to the point of fear, she definitely found them disagreeable.
Furthermore, Yuloli didn't enjoy being active during the day and was relatively more active at night, being a complete night owl.
Of course, this was only a preference she had; it wasn't that she couldn't be active during the day.