Peach is not a "new" monorail. Rather, it consists of the damaged cab cars of Pink and Purple and the (completely or largely) undamaged center cars. Now, just how much is really new in this rebuilt train is yet to be fully revealed - at least the carbodies for the cab cars are new, probably with many new components (reportedly the cab cars may look and feel "new", though again in actuality they are the (more heavily damaged) sections of Pink and Purple). The coaches (center cars), though, appeared to be only slightly if at all damaged in the accident, so may have needed little work for monorail Peach.
Note that while the news report calls this a "new" monorail, the DisneyParks blog instead refers to this as an "additional" monorail train.