How would she obtain it?
Discussion
The invoice contains the preimage. Supertestnet showed me years ago a great simple website to breakdown and decode all the information in said invoice
I'll share with you once I find it again
(Had to use this for an old WoS wallet, worked great to share with WoS support).
Actually the invoice contains the HASH to the payment preimage. Only if you've paud the invoice do you obtain the preimage over the lightning network. It is needed to settle the paynent and it is your proof of payment.
sorry for the late reply. Alice should be able to see the preimage in the sender UI if the invoice was paid. That is your proof of payment. If you don't have it, the invoice wasn't paid.