Hi Laura,
Mark K here, thanks for getting in contact!
I understand what you're trying to do and I'd say there are a few options thankfully, but my personal pick would probably be Follow Up Email. https://apps.shopify.com/follow-up-email
You could also try Email Automation or Remarkety, they both look very useful!
https://apps.shopify.com/remarkety-for-shopify
https://apps.shopify.com/marketing-automation
One of those should do the trick for you!:)
Cheers!
Mark K
Shopify