That is great news! I was going to suggest if she lives near you, invite her over to see how much work it is too care for a bunch of kittens. Like hold off on doing everything like litterbox and feeding and look all frantic for free time which you don't have because you are so busy caring for them.
If she is still really sad about not having kittens, maybe invite her over still and show her (exaggerate a bit) on how much time and work and money it is. Show her your shopping list with all the extra litter and special (expensive) kitten food you need to buy. Show her a calender made up on when all the kittens need all of their shots and the vet bills, and EVERYTHING.
I never understand when people have a female cat who they want to have one litter. Do they just one day go "ok you are in heat so you must be ready to have kittens, go out into the world and get pregnant now, bye see ya later, don't come back until you are pregnant"?
I mean common sense, don't they realize that the random male cats may be diseased? Just like people ya know? You go out and sleep with lots of random people and you just may end up with a disease!