The young girl dressed in red is my daugher.
为什么用dressed,而不用dressing?
因为dress在这个时候,后面要加宾语,正常的用法是：
dress sb 给某人穿衣服.如果其后没有sb,也就是宾语,那dress就要用dressed,这一点一定要记住.
这句话可以这样理 the young girl (who was) dressed in red is my daughter.
同样的用法还有：seat,它当定语时,后面没有宾语时,也要用seated.
The man seated /sitting under the tree is his uncle.