My mother passed away two weeks ago. I am a co-executor as well. Mother's well doesn't mention any of the gifts he has made. He says mother told him to do it. The money and jewelry all went to his old girl friends and people that work for him now or use to. Mother never told me about these gifts and we talked about everything right up to her death. I saw this co-executor nearly every day for the last 8 months when mother was in and out of the hospital and he never mentioned any of this to me either until he says the gifts were all made. There is nothing in writing that I know of either. Mother's will was really simple. All of her property was to be split evenly between my brother, my son, and my self.
Regardless, I think this person has acted in very poor taste and you deserve an explanation. The two of you should be working together; that other person needs to recognize that and get on board and learn how to work as a team.
The issue of the jewellery is probably not about the value of it - it may have a substantial emotional attachment - a cheap locket with hair of your only child may have great significance to you but not to anyone else whereas a diamond held in a bank may have considerable monetary value and may have no emotional tie at all.
And that is why the terms of the will have to be adhered to UNLESS SHE HAD IT WRITTEN AS A CODICIL, in which case it becomes part of the will I suggest you google probate for dummies where it explains that as GA said that as part of the probate process expenses have to be handled first before distribution of assets
Lots of people make bequests that they don't formally include in their wills. Sometimes it can be as simple as telling someone that they may have an item "someday", often for as little a reason as they admired it. Sometimes people laboriously label every knickknack with the intended recipient's name. And sometimes families squabble over every penny, switching labels and hauling off truckloads of possessions they haven't any use for just to keep someone else from having it.
Who's handling any asset inventory?