I have no idea what you're on about. The way the story plays out it seems that it was already established that her granddaughter moved in with her for the express purpose of marrying and living with her (even gave her a flower when she got there, although I'm not sure if it's specifically a marriage thing unique to the world this story takes place or a way to greet a host in Japan). Oni was only hesitant because she didn't want her granddaughter to live a boring life with her, and even at the end you can see that both of them seem to share a similar level of romantic attachment.
Example being:
1. She referred to what her granddaughter did as "pleasuring her", a phrase she would probably not use if the advances were completely unwanted.
2. She seem completely on board with the idea of repeating this every night.
This is a fluffy yuri story, stop trying to ruin it.
anyways is it just me or the characters kinda looks like the girls from...uhhh idk I forgot it's kinda about the "unemployed girl and the landlord" and please let me know what's the title I forgot the title and the plot lmfao