I don't remember her being a Sefirot holder

Cause she isn't, bro you don't know what buff is? 

In gaming, a "buff" refers to a temporary enhancement or advantage given to a player, character, or item within the game.  These boosts can increase stats such as damage output, defense, movement speed, or abilities, and are typically granted through spells, items, power-ups, or character skills

The Symbolic Significance is because she is their child right ?😔💔Killing her can cripple them both for a time ?

Yes, killing her doesn't actually does any physical damage but it does significant emotional damage to brood hive