(1) Neither it is lawful to demand the expenses occurred in marriage nor it is wajib (necessary) to compensate.
(2) She can accept the mahr amount.
(3) The jewels she got from her parents they must be returned by the husband, while the jewels she received from her in laws if they were gifted she will not be asked to return them and the in laws can also not demand the same back. If the jewels were not gifted or not specified, then it will depend upon the custom of the area; the jewels are borrowed in our area thus they are taken back, if the case is so in your area then the husband can take them back; otherwise not. The husband should return the furniture and articles she received from her parents. If both sides settled to return and receive the existing price of the articles then it is also acceptable.
(4) The matter of necklace should also be settled according to the details mentioned in answer 3.
Allah knows Best!
Darul Uloom Deoband