Wow, that accounting person was still there in the evening - she sure has a long shift! Ah, hospital workers tend to get stuck with 12 hours shifts, especially back in the 90's.
In the first movie there's a closeup of Sil in John Carey's garden where she blinks and we see that she has nictitating membranes in addition to "normal" eyelids. You thought that was just there because it looks cool and alien. Nictitating membranes are a feature possessed only by semi-aquatic tetrapods, so her having them is a subtle indication that she can function underwater for prolonged periods, foreshadowing the scene at the film's climax where she hides underwater to elude the heroes.
Why does Sil need a cocoon? Cocoons are used by animals that dramatically change their shape between the juvenile and adult form, like butterflies. Something Sill doesn't do. Not to mention that she's a shapeshifter anyway; she rearranges her body without needing a cocoon multiple times in the movie.
remember that Sil had rapid regeneration powers, hence why she could survive the birth, while the female astronaut didn't. Though, this brings another Fridge Logic of why the female astronaut didn't turn into a hybrid while Patrick did...
As they were digging that Absurdly Spacious Sewer under the hotel, not a single survey detected the GIANT CAVE SYSTEM?