Well, looks like everyone has already figured out that Ruriko ended up in the hospital for emergency surgery, possibly from appendicitis.
But I am posting something that is very interesting.
So Kurumi got the news and took a taxi to the hospital, and talked to the receptionist.
"Excuse me, Um...Ruri..where is Aisawa Ruriko?"
"Are you a family member?"
"(I am) the wife"
You can clearly see what happens if a country does not recognize same sex civil union or marriage. "Are you a family member?" would ended up with a reply "(I am) a friend", which means the family can veto and ban kurumi from seeing Ruriko. However in real life situation like here in the manga, since Japan has the partnership certification system, with individual prefecture or towns granting the certificate, Kurumi simply need to bring her paperwork and says "(I am) the partner/wife" This however can only be done in the prefecture or towns which grants the certification, where the two of them live. If the hospital is located in another town that does not recognized the certificate, then kurumi is not family. If it is located in a town that recognized another town's certificate as an exchange, then kurumi is family and trumps everyone.
Being partner or "wife" automatically trumps any other relatives when it comes to medical decision making. This is the most important privilege that gay couples want. Renting an apartment with a certificate also means that the potential renters are "spouses" as landlords obviously prefer childless working couple. So yes, Usui Shio just nailed that one. The only fact that is incorrect is that the two persons are not recognized as spouses, but just partners (but still trumps all relatives). But I highly doubt that if a person declared that she is a wife (which is technically incorrect in the legal sense), a nurse or receptionist would refused to give out any information.
So yes, Usui Shio just demonstrated a potential nightmare scenario if a couple does not have the certificate. In the manga the couple actually get the marriage application (ie. license) from city hall. Sensei never did disclose whether the application was completed and send it back to the city hall, or it was completed but did not return to the city hall. One way or another the two of them is still, legally, completely unrelated.