I got the idea of sarcasm because even before her Sotherton remarks and her digs at Edmund with the woman of spirit remark, is "Miss Crawford, a little suspicious and resentful of a certain tone of voice, and a certain half–look attending the last expression of his hope, made a hasty finish of her dealings with William Price...". So I thought she was still annoyed and being sarcastic when she brought up Sotherton. Sotherton is where she first made fun of the clergy and then discovered that Edmund was to take orders. It just seems to fit her personality to bring up something like that.