Hull and slice the strawberries. Zest the orange using a zester or the fine side of a cheese grater. Cut the zested orange in half and juice it.
Whisk the strawberry jam with the orange juice in a shallow bowl or container large enough to dip the ladyfingers. Add 1-2 tablespoons of water to thin if the jam mixture seems too thick. Set the jam mixture aside
Mix mascarpone with the orange zest in a mixing bowl. Set this aside.
Whip the cream, powdered sugar, and vanilla, in a mixing bowl, with a mixer on medium speed, until stiff peaks form. This should take 6-8 minutes but will depend on your mixer speed. Check it after 5 minutes so you don't overwhip it.
Gently fold ⅓ of the whipped cream into the mascarpone cheese mixture to lighten it. Then, fold in the remainder.
Dip the ladyfingers one or two at a time into the jam mixture. Coat all sides. Arrange ladyfingers over the bottom of an 8 x 8 inch baking dish. You may have to cut them to fit the last row. If necessary, spread a little extra jam over the layer so everything is evenly coated.
Spread half of the whipped cream-mascarpone mixture over the ladyfingers.
Place a layer of sliced strawberries on top of the cream.
Repeat layering with remaining ladyfingers, preserve mixture and whipped cream mixture.
Cover with plastic wrap and chill in refrigerator for at least 8 hours or overnight to let ladyfingers soften.
When ready to serve, add the remaining sliced strawberries on top.