<Snipped quote by Proxi>
Where would the middle-ground be? Not being difficult, I'm legitimately asking, because I think that is probably going to be the answer to OP's question.
I always felt it would be awkward to focus too much on referencing physical differences ("She felt the weight of her breasts as she jogged") for the same reason it would be awkward to overuse male differences ("The jungle was so humid his testicles stuck to his legs"). Actually, this reminds me that there is a women who writes historical fiction short stories from the perspective of a gay military officer in the 18th century (I forget her name or the name of the stories), and when reading one of those I was pulled out of the story when she used a line sorta like "As he climbed on the horse for battle, the fear made his scrotum pull tight". It was weird because, though I've been scared of shit plenty of times in my life, I don't think i've every consciously thought about what my scrotum was doing while I was afraid. I feel like it was one of those things she wrote because, as a woman, the idea seems like it would be pretty noticeable and worthy of mentioning, but for men it's sort of a tertiary thing. Likewise I always figured over-focusing on female physical traits can end up distracting.
And I also think too that the line for femininity is kind of complex. There is a line that I figure we all kind of know, but it's difficult for me to try and put into words, so it is difficult to know when I've breached it. I've also, like the OP, been told before that my female characters didn't seem very female (by a woman as it turns out), but she couldn't tell me why, and I can't exactly pin point it either.
For OP, I agree with everyone that a sample would help.
I don't think there is any strict line. I'm just saying she should act like a human instead of just 100% femininity and female stereotypes. The middle ground is to write a woman the way an actual woman acts. She can be girly or a tomboy, but making a character that is nothing but pure girly-ness or so tomboy that there's absolutely nothing female in her behavior are simply unrealistic characters to play as. The same pretty much applies to male characters as well.
The middle ground is simple and fairly large: any character that has focus beyond just its gender. Like you said, focusing too hard on the body parts of the character's gender ruins some of the effect. (although that has more to do with the narrative then the characters themselves) Don't base the personality solely on the gender. Take the personality and apply the gender to it. If that is done, then there's likely to be nothing to worry about. Don't be afraid to make a girl act girlish or a guy act macho. Just make sure that they are still represented as people and that their personalities are more then just whatever matches their genitals.
I really doubt the OP really messed up all that badly to be honest, sounds like the critic was more angry about something else or simply had a different opinion on the "right" way to play as a female character.
As complex as the line is, one thing that is a hard and fast rule is that both genders of humans are people and should should behave like such.
Including one or two REAL stereotypical behaviors (that are actually common behaviors that do happen from time to time) doesn't automatically make them bad, as long as that isn't all the character is. But if you include unrealistic stereotypes that are mostly fictional and designed to insult the opposite gender, then what you've created is not a normal character but instead a mockery of whatever that character's gender is.
And about the last line about your characters not seeming very feminine, then perhaps it wouldn't hurt to think about what they are like to see if they are perhaps a bit too manly in some ways. I've had similar troubles back when I tried writing a male character, but to this day I'm uncertain on how to fix it. The problem comes from the fact that occasionally people compensate too hard to not make their character stereotypical at all. That often ends up blocking the gender aspects of said character. So keep that in mind.
"Jim walked down the street, it looked like it was about to rain. He sped up his pace, not wanting to get his new woolen sweater wet. He thought about what he was doing with his life, and got disappointed. Here he was, no wife or family. It looked like things weren't going too well for poor Jim. He picked up a comic book on his way home, and quickly arrived at his doorstep. Jim sat down on his couch and watched television. He was excited to see that there was a wrestling match on."
Jim likes wrestling, which is usually seen as a male stereotype. However, there is more to Jim then being a man. He wants to take care of his clothes and read comic books and raise kids. He doesn't like wrestling because he's a man, Jim likes wrestling because he thinks it is cool. That was an example if a character who has a gender, but it doesn't fully define the character. And yet at the same time, things males sometimes like to do aren't denied altogether. I'm not afraid to say Jim likes wrestling and thinks it is cool. Because that's not his defining character trait. And some men really do like watching wrestling on TV, so it's not an unrealistic or insulting stereotype. No mockery of men was made. That's how I crossgender RP. Whether or not it's the right way is based partly on interpretation.