I'm so sorry, yes Monkey is grieving. Princess did the same thing when we lost Roxanne. Princess has Poncho to play with, but she kept looking for Roxanne.
Last March we found a good breeder and got Mandy. Mandy plays with Princess just like Roxanne did. But even now two years later, she will get upset over one of Roxannes toys. It takes time for them just as it is for us. They really do have big hearts. Please give Monkey a big YT hug. Maddie will forever live in both your hearts.