How did the gift from Mary Warren work against Elizabeth Proctor?

Mary Warren gave her employer, Elizabeth Proctor, a "poppet" or doll that she made while she sat in court that day.  Mary Warren says, in Act Two,

I made a gift for you today, Goody Proctor.  I had to sit long hours in a chair, and passed the time with sewing [....].  We must all love each other now, Goody Proctor.

This gift seems to be a kind offering.  Mary Warren goes to bed, and...

Mary Warren gave her employer, Elizabeth Proctor, a "poppet" or doll that she made while she sat in court that day.  Mary Warren says, in Act Two,

I made a gift for you today, Goody Proctor.  I had to sit long hours in a chair, and passed the time with sewing [....].  We must all love each other now, Goody Proctor.

This gift seems to be a kind offering.  Mary Warren goes to bed, and John and Elizabeth continue to discuss Elizabeth's fears that Abigail will use the trials as a way to get rid of her and secure John for herself.  Soon, Cheever arrives with a warrant for Elizabeth's arrest: Abigail has indeed accused her.  He asks Elizabeth to hand over any poppets she keeps, and when he lifts the skirts of the doll and sees a needle stuck in its belly, his "eyes widen in astonished fear."  He says, that night, that Abigail Williams sat down for dinner at Reverend Parris's house and suddenly,

[...] without word nor warnin' she falls to the floor.  Like a struck beast, he says, and screamed a scream that a bull would weep to hear.  And he goes to save her, and, stuck two inches in the flesh of her belly, he draw a needle out.  And demandin' of her how she come to be so stabbed, she -- to Proctor now -- testify it were your wife's familiar spirit pushed it in.

Mary Warren soon reveals that Abigail sat beside her in court and watched her make the doll and push the needle in, for safe-keeping.  Proctor and Elizabeth now understand that Abigail has used this information to frame Elizabeth for witchcraft.  The poppet plus Abigail's testimony that Elizabeth sent her spirit out to push the needle into her belly, called spectral evidence, is enough to convict her.