Personally, I'd pre-empt her.
And by that, I mean that every time I had something new at work, i'd mention it before she could. Big, big smile and cheerful tone, and a "Good morning, Hyacinth. Now, I know you're always interested in the cost of the things I buy... this item is new. I got it at ThisShop for around X price and I'm perfectly happy with what I spent on it. Isn't it pretty? Now, i'd better get back to that bean dip project..." Bigger smile and walk away.
Do that every single time. The game's then yours and she'll soon give up if she realises she won't get a rise out of you.