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My name is***** and I will try to answer your question tonight. Based on the fact that she has not yet had a heat cycle, it is very possible that she is sterile. The most common cause of this in cats is being a hermaphrodite- having some parts male and some parts female (ie testicles internally with a uterus, or some variation of that). She may also not have developed her ovaries at all, though this is less common.
I would still recommend having her spayed, just so that you can be certain that she is just not a late bloomer. Feral cats can have very cyclical heat cycles and will not cycle in the winter (especially if you live far north) because there is not enough food to support a pregnancy and nursing kittens. Most queens will start cycling in February and March for April and May kittens, when there is a better food supply.
Does this help? Do you have any other questions?
How is your kitty this morning? Do you have any more questions about spaying cats?
Also, if you would please consider rating my answer, I would greatly appreciate it.