Does a wife married only a few months ago receive the same share of the estate as a wife who was with the husband for decades?

Yes, the wife's share in faraid is divided equally among all lawful wives, regardless of how long each marriage lasted. The one-eighth or one-quarter that is the wife's right is split in equal portions, whether a wife was with her husband for a month or forty years. For a first wife, this fact can feel bitter. But faraid is not the only channel. Your contribution to property built up together can be claimed as jointly acquired property (harta sepencarian) before the faraid division, and gifts made during his lifetime are also valid if done properly. Gather evidence of your contribution, then discuss the claim with a syarie lawyer or a Syariah Court officer. See matrimonial property (harta sepencarian).