"Day2 inpatient chemo- sleeping a lot, liking new anti nausea med this time, & looking to get home today! #GetWellJen," wrote The Little Couple star, who's fighting a rare form of cancer.
That gave Arnold a chance to spend time with her family, including children Will, 3, and daughter Zoey, 2.
She baked Christmas cookies, shared a cute pic of Will with Santa (Arnold's dad dressed up), and enjoyed a traditional Italian seven fishes Christmas Eve dinner that her husband, Bill Klein, whipped up.
"There are moments I feel just terrible," Arnold, 39, told PEOPLE earlier this month.
"I can't believe it is happening. Other times, I feel like this is just a bump in the road."