Hi and welcome
Is it an ovarian cyst or a skin cyst? Skin cysts are a comparatively easy, low risk operation with very good recovery chances since your vet doesn't have to go into the body cavity and it is generally a pretty quick and straight forward procedure.
My Hafren was just one month short of her 7th birthday when she needed a huge burst 5 cm cyst with fleshy inclusions removing that unfortunately had put on a real growth spurt and promptly burst while my piggy savvy vets were away on their summer holiday - we'd had it under observation for two years and were hoping it would stay put in view of Hafren's age but unfortunately, the cyst didn't oblige. Nevertheless, Hafren made a full recovery and lived to celebrate her 7th birthday despite being a very elderly guinea pig at the time of her operation and the op more complex than expected. I hope that gives you some courage.
Hafren with her fresh operation scar - it was by far my biggest cyst op ever with my oldest piggy but it all healed well, if a little more slowly, and she went on to live for a few months more to die basically from old age.
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The oldest sow of mine needing a spay for ovarian cysts was around 6 years and also lived to see her 7th birthday.
In comparison, your own piggy is in the prime of her own life and unlikely to have a large, unusual cyst needing a longer op so if my Hafren as an extreme example was able to make it through, it should be a lot easier for your own youngster.
If you have anxiety issues, please refrain from any online research in the future. Always keep in mind that what you find there are inevitably all the horror stories and the miracle cures but you will
not find is the vast majority of perfectly good normal outcomes because they are just taken for granted and are not considered worth posting about. This means that unless you are aware of the strong bias, you will always get a very distorted picture which will only serve to feed your anxiety but not contribute in any way anything positive to the problem.
Operation practice in small exotics has improved massively in the 15 years this forum has been running. We frankly don't see many posts about piggies not making it post-op anymore on here, which is a much better reflection of reality than what you can find with targeted research.
Here is some very practical information that you may find helpful:
Tips For Post-operative Care
Pet Owners Anxiety - Practical Tips For Sufferers and For Supporters
Please take a deep breath and all the best!