Aww, that sounds so cute that Filli is acting like a momma rat :).
My girl cat (in the avatar) was a teen mom cat (very good mommy who fostered two additional kittens who had no mommy). I often wonder even though she is spayed, if her mothering instinct would kick in again if I plopped a kitten in front of her.
My grown dog who was spayed young and never had babies LOVES puppies and acts like a surrogate mom (or big sister).
1 Doberman Mix: Emmy, 2 DSH Cats: Rowan & Jacob, 1 Bearded Dragon: Rainier (aka Mista Lizad Man), 1 Eastern Box Turtle: Greta, Two 5g tanks: Alchemy (Halfmoon) and Custard (Yellow VT)