Thank you for your question.
I have to admit I am very familiar with this challenge (having 2 female rescue kitties with mysterious histories). And it isn't nearly as easy as with male cats (since there is nothing to see outside to give us a sign).
If Prettygirl is a young cat then first thing to do is to check her midline abdomen region. Sometimes you may be able to see a spay wound or feel muscle scar in the area. If she has been a rescue kitty, some rescues will put chromic cat gut when closing their muscle layer. The reason is that this doesn't break down with healing like normal suture would, and leaves a palpable sign of a spayed female (since its so difficult to tell if they have been).
If you don't see any signs of these, then its a case of wait and see. I would advise keeping her inside initially (and away from unneutered males), because unneutered females do tend to make themselves known quite quickly. This is due to their quite noticeable and frequent heat cycle. They usually have between 2-4 estrous periods a year, but in an unmated female they tend to keep coming back into heat every 2-3 weeks. So, if she starts yowling with her bottom in the air, then you will know that she is in heat and not spayed.
This is a challenge for vets and owners of rescue kitties with unknown histories. And sometimes we find these cats booked in for spays, but find that they have no uterus when we come to do the operation (just little remnant stumps from their previous spay). So, the best thing to do is to have a look and a feel of the midline, but if nothing is giving you a clue then it is a case of waiting and seeing.
I hope this information is helpful.
Please let me know if you have any further questions.
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