Ascites is a symptom of another underlying problem. Reproductive issues like salpingitis, internal laying, cancers, EYP can cause it. Also organ failures can. Sometimes draining the fluid can make them more comfortable for a time, but the underlying condition will remain and the ascites will probably recur. Also draining too much fluid to quickly can put them into shock and can be fatal sometimes. Only you can decide based on what you are seeing if attempting to drain is worth it or not. If you choose to drain then do so slowly and only a small amount. Usually the puncture will continue to slowly drain/drip for a while, which seems to be the safest way with less chance of shock. You can search for threads where it's been done for more info. The only way to know for sure what the cause is is to either send her off for necropsy once she is gone, or do an informal one yourself. Sorry the news does not sound better, the long term prognosis once they develop ascites is not generally good.
