IMHO, I wouldn't give her a gift. Just a nice card with Merry Christmas and that's it.
MAYBE help your son pick something out (that you have narrowed down first, so he picks the "blue one" or the "green one", etc) and maybe he can take some pleasure in giving.
Not sure if he's old enough to recall it but if so, maybe that. Sign "From Son"...
M: 57 H: 60 M: 35 yrs S30,D28,D19 H off to Alaska 2006 Recon 7/07- 8/08 *2016* X = "ALASKA 2.0" GROUND HOG DAY I File D 10/16 OW DIV 2/26/2018 X marries OW 5/2016
