It's smart how she had the finger pointed at Emma rather than Mielle. While Mielle of course was part of it, if a mere servant pointed to her it would just end up as her trying to defame her old master and no one would credit her testimony. Especially since Mielle still has a good reputation in the house, no one would buy it. However Emma is a fellow servant and wouldn't be subject the same esteem. She's also Mielle's greatest ally and conspirator besides Lady Isis, so getting rid of her would be a big blow to Mielle' power.