She is deffinitely too small to breed, especially if she is already over 15 months of age. If she is still under 14 months old, I would suggest concentrating on getting her bigger by offering a well balanced diet and making sure she is parasite free etc, to hopefully get her to grow more.
Though she may have good color etc. if she is already an adult and all her past husbandry was perfect (thus eliminating this as the reason she isn't very big) her smallness is most likely due to genetics, either a defect in her genes itself, problem with incubation, a late bred female (mother) etc. Though her babies may be more normal sized, if the cause is genetic and you find a male the same size, the babies could be just as small if not smaller. Thus you will have under sized babies.
To determine if she was just the runt of the litter, see if you can find out how big her parents and siblings were. If they are all quite large, then breeding her may not be a problem. If they are all or the majority are on the small side, it would not be a good ideal to breed her.
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PHLdyPayne