The American has started work on a musical version of Chris Van Dusen's hit new Netflix show.
So far it includes original songs based on the show. Other users can add their own verses using the app's Duet feature.
Barlow and her writing partner Emily Bear have "big dreams" of turning it into a full-scale production.
"I've always posted my original music on TikTok so this was no different," she explained to to BBC Radio 4's Today programme on Monday.