Aww don’t trade her in for a new one! She is still just a baby, give her some time she may just surprise you. While 6.25” does seem a little smaller then normal, it is not that far off. She may just need some more time then others to reach full size. One of our females (above as a baby) was a little runt when we bought her, and we honestly did not think she would reach full size let alone breed. However she proved us wrong, it took 2 years but now she is 8”. We may attempt to breed her this year for the first time. So do not give up on her, she’ll get there eventually.