The Witchcraft that Caster uses is all physical phenomena performed with her own body. While common Magecraft are programs that "recompose what exists around," Witchcraft are programs that "recompose the raw materials in one's own body."

According to Caster's own word:

"This time there is only one due to the constrains of the Moon Cell, but originally I could produce a million troops from my multiple tails!"

That is really suspicious though.

Fate/EXTRA Tamamo-no-Mae (Caster) Matrix