She expressed her excitement over Twitter at the time.
Recalling the experience in a later interview, she shared: "My sister gave birth in her living room and I got to be kind of like an assistant doula which, in a home birth, is kind of just there for support.
"I was in it! I mean I was holding ... I probably shouldn't give too many details, but my sister actually is a true rock star. She gave birth in her living room without a single Advil!"
Katy also filmed the entire delivery on her iPhone, but Angela didn't want to watch it initially.
The news of Perry's latest birth duties comes after she admitted at the weekend that she would be happy to put her differences with Taylor Swift, with whom she has had an ongoing feud with since 2012, aside to work with her on new music, if the Shake It Off singer apologises for her past behaviour.
When asked if she'd ever work with the Blank Space singer, Perry said: "If she says sorry, sure!"
- Bang! Showbiz