Grace wasn’t optimistic about the Swifts, but Bianca was different. Even though Bianca and Pearl had a great sisterhood, she didn’t know that in the elimination of the Millers, her own family was also involved.
Bianca was a sweet, naive, jolly, and cute girl. She wasn’t someone who would deliberately harm someone else. She was very pure. This is why she was kept out of everything that happened to Millers. Those three brothers of hers were the ones to do all the dirty deeds.
Since Bianca needed a job, she could give her one.
Firstly, Grace knew a lot about Bianca’s character, so she knew Bianca could be trusted.
Secondly, by hiring Bianca, she would be indirectly helping her. So, later, the Swifts will not lay hands on Millers without a second thought.
Thirdly, even though Pearl is now not accepted by the Smiths, if she got help from the Swifts, she might be accepted by the Smiths.
