"Selina's attitude in this pic is so strong and self assured, and I love the way her eyes look. Sometimes, I feel like I'm not doing art, so much as capturing a glimpse at a real person, somewhere."
You said a mouthful there. Perfect description.
And although I fancy the Kitten's Funbags to be of generous proportions, I think you are absolutely correct in your interpretation of what a "realistic" Prowling Pussycat would, could, and should be like.
(One of the reasons I enjoyed Michelle Pfifer as the first Kitty in the Bat-Flix.) Lithe body, more athletic and as you put supple and gymnastic.
Lovely little kitties compliment the attitude here very well, too.
Indeed, there are two main concepts for Ms. Kyle.
Gymnastic
and Gymnasty.
This gal's got a bit o' both.
Someone out there would be very pleased with you capturing her essence so well.