So, I won't profess to be an expert on Beatriz de Bobadilla, but I do know the early Americas and I did some digging for you. If there's any expert on the matter, feel free to correct me. Also just a heads up most of the sources I looked at are in Spanish (since I'm going to assume you looked at the English ones), so If you want translations on any of it just let me know.

To start, it looks like most of what I've found indicates that her relationship with Columbus wasn't exactly the truth. In "En busca de la verdad: Algunas mujeres excepcionales de la conquista" by Juan Francisco Maura, he indicates that the supposed relationship depends on "un documento cuya autenticidad se pone en duda" (a document that's legitimacy is uncertain), and that, although it's a nice story, it belongs more to plays and literature. He also doesn't mention her death at all. He also references a number of other Spanish authors who have written on the topic, and it seems like that there's some doubt over the validity of her relationship with Columbus, which is corroborated by the few other resources I could easily find on her. I realize that's not necessarily answering your question, but I also haven't seen anything regarding her and poison. Could you potentially link your book/put a picture up? It would help a ton in finding more if you still want me poking through Spanish sources.