swelling in the knee

My mare which is 12 this year keeps having this swelling on her front knee. And the swelling stays on for a long time. She doesnt limp when she has it. The vet takes out some infection with a needle. Is there anything I can use ?
**tried arnica gel. Didnt work

Does it come and go? Or has she had if for a length of time? Did you notice what color fluid came out when your vet drained it?
If your vet thinks its an infection then you would probably want to put hr on antibiotics, draining it every now and then won't cause it to clear up I'm afraid. You don't want it to go systemic. Has the swelling gone up her leg at all?

Do you have pictures?

I don't have pictures sadly =( the infection is transparent. The swelling never got up to her leg. Only the right front knee. The vet says she probably hit it in her box. But I don't think so. She's really well tempered never messes around in her box. We 've used antibiotics. Thank god she didnt have for since 2 months but im curious if I can use anything to avoid it ?

*i give cosequin powder with her food every day.

The fact that the liquid is clear indicates it could be joint fluid, which isn't a good sign, but not always worst case scenario.
Swollen Knees

We have had good results with Surpass, a topical anti-inflammatory.
Surpass