My daughter is using a fairly-recent-model iPhone which is almost certainly up to date with software on Skinny Mobile; I am an Android user on a device that's running ColorOS 13 currently on 2Degrees.

For the last week or so, all SMS messages I send her are being received multiple times on her device; she says about 1 minute apart.

This sounds like her phone isn't confirming receipt back to Skinny, so the network is re-trying the message - at least by my rough idea of how it works.

Any suggestions for things she could look at to resolve?  I'm assuming it's an entirely receiver-side issue and that I don't or can't check anything specific.  But can my provider?  (2Degrees?)

I will, of course, suggest to her that she touch base with Skinny customer support if she's not done so already.

Ideas welcome!