Will deleting a device from iCloud remove data from that device? I bought my sister and iPhone and used my Apple id to help set up her phone. Now I want to delete her phone from my iCloud so she can set up her own Apple id. If I delete her device from my iCloud will it affect or remove any of the data on her phone?
Removing the phone from your iCloud 'find my' structure won't in itself remove any data from the phone…
…but re-assigning it to a new owner will. It will have to be set up again from scratch.

As the phone is currently owned by your Apple ID, so are all the apps &amp; the data stored within them. You can restore [most of] the apps, music etc if you set up Family Sharing but any data in those apps will not be transferred with them, as it still belongs to you.