Wow, that really took some doing to finally figure this out. Makes total sense- it was so frustrating to keep putting her thru medications & their side effects. It's a very rare issue, & even if the tissue found isn't currently cancerous, it might still be best to remove it to prevent that possibility, or further abrasion that could cause a lot more bleeding suddenly (like if she swallowed a bit of something she couldn't digest, the bleeding might be severe from trying to pass it). You're a great owner for sticking with this to get to the bottom of the mystery, &to your vet also.