Memorial tributes can be difficult to deliver as you're trying to condense a lifetime of achievements, experiences, feelings and friendships into one short speech. What you include in your tribute will depend on the person who has passed away and your relationship with him. Throughout life the person will have had trials and triumphs, wonderful experiences, great friendships and, hopefully, true love and you will decide which parts of her life to explore in your tribute.
Use someone else's words if you can't find your own. Depending on how close you were to the deceased it can be impossible to try to express yourself in a time of grief. If you don't think you can sum up what this person meant to you then don't be afraid to look to other people for inspiration. If singing and music played a huge part in your choir member's life then find a quote that sums up her love and passion. Music is a universal theme and everyone from Shakespeare to The Beatles have written poignantly on the subject.
Talk about your shared experiences. Anecdotes and stories make up a large part of most memorial services as they are one of the best ways to illustrate the personality and character of the person you have lost. It is likely you and your choir members will have a host of happy and meaningful memories and shared experiences; mentioning a few of them at the memorial will be a great reminder of the times you spent together.
Sing. If it's appropriate to do so, then you and your fellow choir members can make no better tribute than to sing. It's likely that your choir member had a favorite song that was dear to her heart and singing it is a perfect opportunity to celebrate your shared love for your choir.