How does Abigail influence the court so effectively?

It doesn't take much to influence the court because the court already believes the allegations of witchcraft; Abigail simply continues to feed the frenzy. She reverses her denial of the existence of witchcraft and indulges in "acted" behaviors that support what the court believes. You have to remember how easy this is for Abigail to do........ she's been getting a lot of pratice. Her mainpulation of the court, in addition to Putnam's adds to the hysteria the townspeople have succumbed to.

When Mary testifies that the girls pretended to see spirits and faint........ Abigail Abigail shudders and claims to feel a cold wind...... so do the others, after which they claim it's Mary's spirit that attacks them.