Headcanon: For all the Touhou jackassery, for Yuuka to be SAD is heartbreaking not only for us, but the usually jerkass population of Gensokyo.
What happened was a relatively rare sharing of information and cooperation that led to a spell-session. Everyone was there, Yukari; Eiren, Kanako, Suwako, Patchouli, etc. Others were allowed, but these did the heavy work. Their goal, transmute "chibi-Yuuka" from sunflower into a body that would not die or replace the current Yuuka.
Some had suggestions that were ignored or vetoed. Remilia suggested turning her into a vampire; Alice suggested a doll. Finally it was decided to implant a philosopher's stone into her chest. Patchouli could make partials, but through the help of several gods and reality warpers, they were able to make a complete one.
Oh, it's Mama.Mama?Mamaa-Mamaaaaa...It's Mama-san.Well, it is fine when it's just us two, but when there are other people around, it's a little embarrassing......Listen, this mama thing, can you stop it when we're outside?Mamaaa-Oh, really, mama-san.