"She is happy to be home with her kids again," a source says of the actress, 37, who returned to L.A. on Monday after her April 19 arrest in Atlanta for disorderly conduct and her husband Jim Toth's DUI arrest the same night.
Her older children, 13-year-old Ava and 9-year-old Deacon, had been staying with their father, actor Ryan Phillippe, while Witherspoon was on location in Atlanta shooting the drama The Good Lie.
"She didn't feel good about being away from them after the news of her arrest broke," says the source. "Her kids are everything to her." As PEOPLE reports in this week's issue, a worried Witherspoon called her kids to tell them what had happened after the arrests.
Another source close to Witherspoon says she remains "mortified" by the incident, and several who know her well say they are surprised she let the situation get so out of hand.
"She's a fun girl who likes to have a good time and let loose every now and then," says another source. "What's shocking is she didn't rein it in enough to keep herself out of trouble. It was a really bad decision on both their parts and trust me, they're evaluating that and they will make damn sure it doesn't happen again."
As for Toth, 42, the high-powered CAA talent agent is widely known as "a big social drinker," as an insider tells PEOPLE in this week's issue.
But the couple, who are parents to 7-month-old son Tennessee, "are seen as very solid," says an industry insider. "They’re very well-liked."
On Wednesday, Witherspoon sipped water with her salad at a business lunch at the Beverly Hills Hotel, while Toth returned to work at CAA.
The pair are due to appear in court on May 22 in Atlanta, where a typical plea deal in a DUI case such as Toth's would involve fines, 40 hours of community service and 12 months of probation, says Ben Alper, an Atlanta criminal defense attorney who is not affiliated with the case.
Witherspoon, who has wrapped the Atlanta portion of The Good Lie, would most likely face community service and a small fine, says Alper.
She has already issued an apology, admitting, "I clearly had one drink too many and I am deeply embarrassed about the things I said" to officers.
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Reporting by HOWARD BREUER, JENNIFER GARCIA and MELODY CHIU