Is it from tip to start of tail or from tip to tip the way you are measuring?
There is no "exact" number if crickets she should be eating, nor can you be 100% positive it is female yet. At the age the beardie is at, it should be getting 2-3 cricket feedings a day, each feeding as many crickets as she can eat in 10-15 minutes. The crickets should all be smaller than the space between the eyes. She "should" easily be eating 30-100 crickets a day plus misted salad in the morning.
You'll have to discover your beardies favorite fruit, veggy, green, etc. But green bell peppers and apples are ok on occasion. Check out this site for a list of foods you can add tot he salad, its color coded: http://home.comcast.net/~holachapulin/Nutrition.html
To get her on eating salad, try mixing a scricket with no back legs to the salad.It wont be able to escape, and she will see movement and try to get it. Most likely she will get some salad in her mouth with that cricket, and realize its tastes yummy! you can also put a freshly molted mealworm in there, but I think a cricket withno back legs is better.
You can also try taking some salad, espicially bright items, and move them in front of the beardie. She should get intersted and may try and eat some.