Compared to Sunny Celeboodle, Selena has much higher health and deals damage per hit, with no delay between attacks, but has one additional knockback and significantly shorter range. She also a 100% chance of knocking back cats and a 40% chance of slowing them.
For the most part, the same strategy that works against Sunny Celeboodle also works against Selena: meatshield non-stop while slowly whittling down her health with long-ranged attackers, including Bahamut Cat and other heavy hitters. Avoid using short-ranged units like Titans against Selena, as they will most likely be killed or knocked back repeatedly before they have a chance to attack. Also, if you time Bombercat correctly, she will be unable to move.