Snare of Serpents by Victoria Holt

Snare of Serpents - Davina Glentyre’s governess is dismissed on charges of theft. The governess is replaced by Zillah Grey, a very unlikely governess. Within a very short time Zillah is married to Davina’s father and again shortly thereafter her father is poisoned and Davina is the accused murderer. Throughout her trial, the public believed her to be guilty, but the verdict is “Not Proven.” To escape public scrutiny, she changes her name and eventually escapes to South Africa where she is caught up in the Boer Uprising.