She must channel her obsession into being the very best slave she can be, for you, by your standards and rules. Then her obsession will benefit you both.

YOU must assure her (somehow) that she pleases you very much and that she is in no danger of losing you as her master. Her jealousy stems from the thought she might lose you. IMO, all jealousy stems from fear of loss. Her own words confirm this... that she feels inadequate and that it is inevitable you will find a better slave. This means that somehow, you have left her insecure.

That said... to 'propertyof..." I say, you have to believe your master when he tells you of your worth to him. In fact, telling him you are inadequate despite his reassurances... just may convince him you're right. So stop doubting yourself. He's owned you for three years. That''s nigh on 30 vanilla-years in an ordinary relationship. Time you relented and take his word for it. Afterall, Master knows better than you what makes a good slave.