My child used to love avocado but she hardly takes a bite now. How to re-introduce the fruit again?

Usually when it comes to introducing solids what you want to do is introduce new foods in the morning so that if there is a reaction she has the day to recover a bit. Always give several days (at least 3 but maybe up to a week if you know she might react) between adding new foods so that you can isolate potential problem foods. It really helps to keep a log as well so you can refer back to what you've introduced and what reactions there might have been. If you notice that a particular food causes a problem, stop it immediately and give it a few weeks before trying it again.