All that's left inside her is "love". Usamaru was the first present she received from her beloved Oriko. The same deep affection she has for Oriko, she has for Usamaru as well. She will do anything in the name of that "love".
All she has left is 'love.' This is the first gift she's ever received from someone she loves, and she can do anything for the 'love' that has the same affection she gave to.