In Vanity Fair, did Becky Sharp actually kill Joseph Sedley?

Just need some clarification to aid my exam revision.

What I got from my textbook is that at the end of Vanity Fair, after Joseph Sedley came to stay with Becky Sharp, he died on a mysterious circumstance. Becky then spent the rest of her time living the life she wanted. There was no indication that Joseph’s death was linked to Becky. However, I got some materials for the exam revision provided by the teacher. One of the analysis of the story claims that Becky was guilty of murder.

I know Thackeray might want to let the readers think that Becky was the one who killed Joseph, but there is no evidence for that in the story. Is it OK to call her out for murder when it is just a theory with no concrete evidence? Although that may actually be what Thackeray was thinking.

And yeah, I haven’t had the chance to read the whole book. That was just what I got from my textbook’s synopsis. Feel free to correct me if I’m wrong.