During the short hearing, Louise Tongue, 37, admitted one count of administering poison so as to endanger life.
The court was told that the poison administered by Tongue, of Caperns Road, Dinnington was morphine, and that she committed the offence on October 7 last year.
Judge Paul Watson QC adjourned the case to allow for a pre-sentence report and a psychological report to be prepared, and granted Tongue bail until the next court date.
"The court needs to know a great deal more about you before it can deal with you," said Judge Watson, adding: "The fact I'm asking for these reports and the fact I'm giving you bail between now and then should give you no indication of the outcome you can expect.
"On the face of things, this is a serious offence to which you have pleaded guilty."