A spaniel without the chase problem
The worry with most dogs and cats is pursuit, and it is the worry a Cavalier King Charles Spaniel largely removes. Cavaliers were bred as companions rather than hunters, and although they enjoy a garden scamper, they rarely fixate on a fleeing cat the way a terrier or sighthound can. Their approach is social and a little wistful: a Cavalier tends to sidle toward a cat hoping for company, read the cat's refusal clearly and retreat to try again later. Size helps too. A Cavalier is close to a large cat in weight, so she cannot easily bully or injure a cat by clumsiness, and most confident house cats size her up and decide she is acceptable within days.
Setting up the first meetings
Even with an easy breed, let the cat set the pace. Start with scent: rub each animal with a cloth and place it under the other's food bowl, so the new smell arrives attached to something good. Feed them on opposite sides of a closed door for a few days, then let them see each other through a baby gate while both are fed or given treats, keeping the Cavalier on a lead so she cannot rush forward in friendliness. Only when the cat eats calmly in sight of the dog and the dog can look away for a treat should they share a room, and even then the cat needs an escape route upward: a shelf, a cat tree or a door left ajar to a dog-free room. Keep those first shared-room sessions to a few minutes with the Cavalier tired from a walk and settled on her mat, so the cat learns the dog at her calmest rather than at her most eager to make friends.
What daily life together looks like
Once settled, this pairing often becomes genuinely affectionate. Cavaliers seek warmth and company, and many end up curled against the cat they once courted, while cats appreciate a dog who does not loom or lunge. Keep the practical separations that protect the peace: feed them apart so the Cavalier, who adores food, does not finish the cat's dinner, keep the litter tray somewhere the dog cannot reach, and give the cat one room that stays dog-free so she always has a retreat. Watch the Cavalier's long ears around a playful cat's claws, and step in if the cat starts ambushing the dog, because a gentle spaniel will usually endure teasing rather than object to it.
One household, one set of notes
Introductions go wrong most often when different family members follow different rules, one letting the dog loose early while another is still doing gate sessions. Agree the stages as a household and write them down where everyone can check. Family Sharing in KinsLe lets you give the teenager and other relatives you choose access to both pets' profiles, so each stage of the pairing is overseen by included family and progresses at the cat's speed.