If I read this right, you're pet sitting Pepsi for an extended period, right? And I'm going to guess this is a relatively well adjusted bird who is familiar with you? If that's the case, you've got a nice head start.
The first thing would be to get all the information you can from your friend as to likes, dislikes, habits, fears, etc. Stick to Pepsi's version of normal as much as possible. Once things seem to be going well, you can explore how Pepsi feels about some of your ideas for food & activities. Be aware of her reactions & don't force anything. If she's an older bird, especially, she may not be big on change. If you don't feel confident about her reaction, ask for advice.
There will probably be moments like sitting for a 4 yo who's over tired or on a sugar high or missing her Mommy or just having a cranky day. Other than that, treat her like a spoiled grandchild & have a great time with each other!