There are already four designations:

"Baby fat," "flabby", "heavy" and "very fat."  

Why are none of those applicable?

...rude to heavy women by using "flabby" and "very fat" then thin women should be treated the same way.

Same terms can mean totally different things to two people brought up in the same culture but decades apart.  In my Dad's time a fag was a cigarette, in my time it was an insult to homosexuals, today's kids view it as an insult to loud bikers from South Park.  Yeah, that's a reach if you don't watch South Park, so let's put it into hobby terms:

Baby fat is a term I associate with a woman who's given birth and still has some of the maternity weight.  Other guys look at it and think of a chubby girl with a few extra pounds.  Other guys look at it and think of some other body type.
Yet this term is the only one TER recognizes for what I'd consider a curvy woman.

Beauty is in the eye of the beholder, and we have to agree on common definitions in order to describe our views to someone else.  My beauty is not yours, but if we agree on using "baby fat" then I can live with it.  Political correctness aside, just pick one that everyone can handle and move on

I don't take offense to any of the size listings that are up now, but I do think there's some confusing overlap.  

For example, I can't decide if I'm thin, average, or athletic. I don't feel like a twig, I'm in shape but I have some curves. But, I certainly don't feel like I look like a real athlete when all I'm rocking is a four pack vs some of the body building or martial arts ladies that are here who are truly athletic. So, I go with average, which could be accurate if you're looking at what someone is supposed to weigh, but I think we can all agree I am not the "average" American woman.  

Then, what really is the difference between chubby and babyfat? My personal definition is that they're both a little overweight, but if you search those criteria, everyone's obviously got their own ideas. Not to mention, this site is supposed to be for the guys. Most don't consider themselves "chubby chasers". They just like a woman with some meat on her bones instead of someone they feel they're going to snap like a twig.  

This isn't a PC thing, it's a maximizing the use of TER as a search engine for both providers and clients thing. If the categories aren't clear, then people aren't going to find all they're looking for.  

I would propose:
Petite (short and small)
Amazon (tall and solid)
Thin/slender
Some cushion (for the pushin) or average
Small BBW  
BBW

Even if you think BBW is just sickeningly PC, it is a commonly used marketing and search term. If that's what the people interested in it and the ones providing it are calling it, you might as well let it be easy to find each other.

The body type description should focus on of the " firmness" or "body tone" as opposed to "body fat" which most likely refers to being :flabby".  Would suggest using the term "firm, full-figure" to indicate the person is above average in terms of body size, BUT, considered to be physically fit as opposed to " flabby". This would be a much more accurate description of AA women whose physiques/body contours are significantly different those of women of other racial groups. Doubt that this will happen because the primary "judges" are white guys who use their standards of what is attractive which compares how other women stack up to how they compare to white women. Whenever I submit a review on large AA women, the choices given by TER to describe her physically is difficult because none of the option are even close to giving a fair description of her.

Support the inclusion of the term "FIRM, Full-figured" to describe body shape. For BBWs body "firmness" or "Body "Tone" is a more  ACCURATE  indication of how "attractive" the lady is thought to be. "Flabby" , "Baby Fat", and "Chubby" are generally viewed as negatives;  on the other hand, Good body tone is always perceived as a positive attribute regardless of body size (slim, skinny, average, or large).