Hi there, Donna!
Coming in on the tail end of the summer, there are a couple of options for you!
September is Fall Flavours month on PEI - a month long festival of sorts focused on Island food, produce, seafood, beef and everything in between, highlighted by celebrity chefs! Tons of events happening starting in early September and a lot of the events have a musical component to them - since there are too many to list here, you can see all of the events here.
Another I’d recommend would be the PEI Beer Fest - happens in Charlottetown on September 8/9. Over 100 beers and ciders, over 30 breweries, and live entertainment through each session. More info and tickets can be found here.
One more option is the Indian River Festival - a summer-long music festival in a beautiful church in central PEI on the north shore. They have one date available during that time period - September 3rd - with two incredible East Coast acts. The venue itself is also incredible! More info and tickets here.
Hope that helps!