Thankfully I had planned ahead, so I had a brand new package on-hand in case of a situation like this. But to my dismay, she wouldn't eat. I tried her regular food (Saki-Hikari) and some Repashy gel food too, but she didn't take notice. The other three were eating energetically all around her while she just hung there, oblivious. So I immediately ordered some oxolinic acid, which is what all the goldfish breeders recommend for bacterial infections, and hoped it would arrive on time. But sadly, she passed away the next day. I'm pretty sad because she was my favorite one out of the bunch and I feel terrible that I couldn't help her. Since then I've been keeping a close eye on the other three and I have noticed some very slight lethargy and maybe some super minor fin rot beginning (these fish are so small and fast it's hard to tell). So I started them on MediGold just to be safe. Luckily they are nowhere near as sick as Specter was and they still have good appetites, so I'm thinking everything will be fine for them.
Specter was the most outgoing of the group and was the first one to start pecking at the sand and the fake plant in the tank. She was sort of the ring-leader; the one that the other fish followed around. Rest in peace Specter, I didn't get to know you for very long, but you will be missed.