Court documents say Rodriguez-Miranda began planning after her brother, his fiancee and their 11-week-old daughter moved in with Rodriguez-Miranda and her mother in January 2017.
On Jan. 12, Rodriguez-Miranda's mother found a series of text messages between Rodriguez-Miranda and her boyfriend, court documents said.
The suspect talked about poisoning the child's breast milk that was stored in the refrigerator to get back at her brother and his fiancee for moving in.
"I’m gonna crush up some of these pills since she decided they can stay longer and kill their baby," Rodriguez-Miranda says in one of the texts, according to court documents.
After reading the messages between her daughter and her daughter’s boyfriend, the mother went to the refrigerator and found two baby bottles.