Sooo if Skitter was a servant what would be her class? I'm not versed in Nasu lore but I feel Skitter can count as either an Assasin or Ruler depending on how one interprets her bug control and fighting style.
Of the standard 7 classesSkitter's aligns well with Assassin, Caster, Rider, and Berserker. She could also count as an Archer but that would probably be her least synergistic class. Of the extra classes Ruler and Foreigner are the only classes she could possess.
Assassin is very easy to see would probably focus on the use of small amounts of highly poisonous bugs and bug clones. Also presence concealment and independent action both fit well with her.
Rider because while all forms of her would have some riding skill due to her experience with Bitch's dogs and the flying machine that Defiant made her, she also has decent charisma. Also Atlas would make a hell of a Noble Phantasm.
Caster due to her skills if Item creation and control of familiars. It would also be cool to see how an author could adapt Territory Creation into her Skillset.
Berserker because she killed Alexandria and Tagg when she lost her sainity and losing your sainity sometime during your legend is all that's required for the Class.
Archer which while the least synergistic class I believe would fit her because she would possess a Clarvoyance skill and the fact that two of the most personal kills she made involved a gun. As well as the fact that she is an acceptable ranged combatant.
First of the extra Classes would be a Kheplr like Taylor with a loss of ego, not much to say here.
And Foreigner because she is connected to an outer god like organism.