Ronza items are expensive, but not all are good choice to buy.
The reason is because we are better off buying these items in the Marketplace for cheaper price, sometimes even below half the price.
Here is the list of Ronza items recommended not to buy at least until she leaves:
Charms
Note: This is a subjective recommendation based on the fact that these items can be sold in the Marketplace and were cheaper than Ronza price in the previous years. The Mousehunt devs might change some of these items not to be available in the Marketplace.
Reference: Ronza items to AVOID until she leaves 2017 edition
Related article: How to get more gold for buying Ronza items