The Oscar-winning actress played dress-up for the four-year-old who is obsessed by her alter ego Elle Woods, and dedicated a photo posted on her Instagram accouont to the fan.
Witherspoon also held up a sign in the picture, which reads, "Get better soon! #TeamWill Love Reese".
The actress added the caption, "This is for one of the strongest little four-year-olds I can imagine. Will - I hear that you're fighting so hard and strong against cancer and that in the hospital you've been watching a lot of Legally Blonde and loving it. I hope it makes you laugh!
Witherspoon, who has three children of her own, is among the list of stars who will participate in the upcoming Stand Up to Cancer charity's fundraising telecast on September 5.
