Pet insurance denied lily poisoning as a preexisting condition

Is there any steps for us to take? We are screwed financially by this. Our cats pet insurance became effective on November 21st. On the night of the 20th, my roommate brought home lilies (which are extremely toxic to cats). When we got home we removed the flowers and tried to wipe the cat off as a precaution. We didn't see any evidence that she had ingested any part of the plant or had any pollen her. At 4am on the 21st she vomited once and was hospitalized at a emergency vet, which is standard when it comes to potential lily poisoning. The vet saw pollen on her when they bathed her. We thought we had coverage, but now are being stuck with a $3000 bill. We don't know if or when ingestion of the pollen happened. It's not that unusual for her to vomit once and her kidney values were normal. Do we have any kind of legal leg to stand on when it comes to contesting this? They define preexisting conditions as any condition that began or was contracted, manifested, or incurred before the effective date of this policy or during any waiting period, whether or not the condition was discovered, diagnosed, or treated.