The 26-year-old singer - who announced she would be divorcing the former Fall Out Boy rocker last week after two years of marriage - has gone to stay with her sibling and partner Eric Johnson, and taken her three-year-old son Bronx Mowgli there while she deals with the split.
A source said: "Leaving Pete was tough for Ashlee and she needed to be with her family.
"Jessica told her she and Bronx were welcome to stay with them until she was ready to find a place of her own."
Jessica and Eric are taking good care of Ashlee and Bronx in their home and are thought to be praying for her to get through the tough time.
The source added to In Touch: "There have been a lot of family dinners and lots of praying. Ashlee couldn`t have asked for better support."
Although Ashlee has gone to spend time with her family, Pete is believed to have taken the break-up badly and spent a lot of time crying about the divorce.
A source recently said: "Pete has been crying a lot to her about this. He is crushed, and does not want it to be over.
"Ashlee is done, she loves him, but she`s ready to move on. When he travelled for work, she had a lot of time to think and in the end just felt happier without him."