Girls vs Boys (continued)

Back in like February or March I posted about the difference between girls and boys. I have a little something to add to that thought......
I, as you already know, am in the "potty training" phase with Kaylee. When we are home she does not wear a diaper, except for naps, and she has done really well the past 2-3 weeks with out any real accidents. There are a few here and there where I just "wasn't paying attention" but nothing to really complain about. I mean she is only 16 months old for gosh sakes. Anyways, so in addition to taking advantage of her not wearing diapers we have also been taking advantage of the lovely May weather we have been experiencing. We take walks every morning, play outside as much as possible, and we even eat outside whenever possible. Back to my point of how all of this is related. So the other day we were playing outside and Kaylee has no diaper on, just her shirt, shoes, and shorts. She tells me that she has to go to the bathroom. Me being lazy again decided to pull her pants down right there in the yard and let her go in the grass. we do live in the country! anyways i have heard NUMEROUS stories of kids going to the bathroom outside. I have done it plenty of times myself. So I pull off her shorts and put her in a squatting position, with me holding her of course, and I tell her it is ok to go. She looked at me like i was a COMPLETE IDIOT!!! She was fussing and telling me over and over that she had to go, but she just wouldnt. -side note: let me just say that i have noticed that she seems to have tremendous control, she has held it for more than 15 minutes before when I just wasnt able to take her--
So she is giving me this "help me, mommy" look and i pick her up and run her inside to go to the bathroom. I put her on the potty and she immediately went, and she looked so relieved afterwards. So off we went back outside to put her shorts back on and play some more. i would not have thought anything about that little event except that last night Mary (my little sis) came out to hang out with us. We were outside playing and the same thing happened, Kaylee said she had to go to the bathroom. So i tried to let her go in the grass again, and again she had stage fright or something so i had to take her in to go. So today i tried again when we were outside and the same thing happened she refused to go outside in the grass and as soon as she was on a potty she would go. so now i am thinking......is she such a girly girl that she wont even pee outside. I mean i know a lot of boys that when learning to potty train (and even after potty training) they just whip it out and go outside. So why wont/ cant she go outside? Hopefully this is not a sign of what is to come. Any ideas or suggestions?