Interesting, I didn't notice the painted belly. What color are her eyes? The paint looks black on both her and the spaniel, and the eyes do look a little "off" I wonder if they are fakies or from another hasbro line?
The spaniel has the right eyes but no white paint on her paws. And I do not know if it's in the right pose or not now, it might be the scrub a dub spaniel baby too...
Swancrossing18 has a complete set of lil litters, I wonder if you pm her she can shed some light on this! I know mlpwhitney, sebby, and partypony have all dabbled in lil litters, they might be worth contacting too!
Sorry for the misidentification!
Eta I found this old arena post with the same bunny! Looks like there isn't a conclusive answer to what she is!
http://mlparena.com/index.php/topic,298880.msg241777.html#msg241777