What are the diagnosis possibilities for a female in relatively good health (some varicose veins)but that has swelling in one leg by knee cap and ankle?

Many Possiblities. Could be related to your vein disease, but also many other possibilities. Some possible venous reasons could be venous reflux disease, phlebitis, blood clots (DVT or SVT), or May-Thurner disease. Also have to worry about pelvic pathology causing compression of veins or lymphatics. Could be lymphedema. Could be arthritis or joint inflammation. Hormonal imbalances. Could be soft tissue inflammation.
A few thing. Medication reaction, baker cyst, dvt, superficial venous insufficiency (related to varicose veins), lymphedema, iliac compression/may-thurner syndrome.
blood clots. Lots of simple, potential causes of swelling in and around the joints (e.g., arthritis), but the thing that comes to mind for me (since you mentioned varicose veins) is a blood clot in your leg veins. What is important it which vein this clot is in (if that is what it is). If it is in a deep vein or a superficial one. With that in mind, i would advise you get it checked out asap.
Deep vein thrombosis. Very likely, a clot in your main vein behind the knee. Get a doppler study. Less frequently, a bakers cyst that riptured, same test diagnostic.