"At the start of the game, Angela's personality is happy and upbeat, saying things like "Good luck!" and giving the Player compliments such as "it means that you are doing good work". She still maintains this demeanor even under grotesque circumstances, such as when she pours a bottle of champagne to celebrate that the Player has killed an employee for the first time. " - https://lobotomycorp.fandom.com/wiki/Angela 

Angelia is a more complex character to explain so if you haven't seen lobotomy corp I def recommend you read the wiki or see some playthroughs before taking her part. Keep in mind she's an Ai built to be the perfect 'everything', Her voice should be cold and monotone but with a hint of spite or sweetness when needed. Don't add any effects to make yourself robotic, she's supposed to be human appearing.