In a new filing obtained by TMZ ... Nicola claims HoundSpa caused the untimely death of her chihuahua Nala -- specifically pointing the finger at a groomer, named Jony Ceballos.

Nicola claims Jony has a history of "intentional and malicious abuse of dogs," further alleging Nala was left injured and in severe physical distress after being treated for a routine grooming in HoundSpa's mobile van.

Nicola is also taking to task HoundSpa and its owner, Deborah “Deb” Gittleman, for keeping Jony on the staff -- even though she says there were past complaints against JC about his mistreatment toward animals.

Per Nicola, she's been left emotionally distressed by the whole ordeal, especially since she witnessed Nala die after rushing her to the vet following the grooming -- and says she treated the pet "like her own child." Nicola claims her other dog, Angel, is also suffering in the aftermath of the grooming, noting the dog shakes/screams from terror when left alone now.

The actress' lawsuit isn't necessarily surprising -- as we reported, Brooklyn Beckham's wife had lawyered up after the loss of Nala -- which she first announced back in June. From the get-go, Nicola pointed the finger at the groomers ... with the events of the tragedy never sitting right with her.

She says she originally posted about Nala's death to raise awareness, but chose to take action when she learned how many other pet owners faced similar experiences at different groomers.

She adds ... "I've dedicated most of my life to saving dogs and I can't in good conscience let this horrifying act happen to more families. I will work for changes and laws to help make sure no one else ever has to experience this heartbreak."