Praise be to Allah.
If the matter is as you said, that the girl was born alive naturally, then she died after ten days, then you do not have to do anything.
The fact that you thought of getting rid of the foetus – as mentioned in the title of your question – does not have any consequences, because the Prophet (blessings and peace of Allah be upon him) said: “Allah has forgiven my ummah for whatever crosses their minds so long as they do not speak of it or act upon it.” Narrated by al-Bukhaari (2528) and Muslim (127).
Neglecting to take medicine does not make one liable, because according to the majority of scholars, taking medicine [or seeking medical treatment] is not obligatory; rather it is mustahabb (recommended) or mubaah (permissible), and because medicine may or may not achieve the goal.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: With regard to medical treatment, it is not obligatory according to the majority of leading scholars; rather a small group of scholars deemed it to be obligatory, as was stated by some of the companions of ash-Shaafa‘i and Ahmad.
End quote from Majmoo‘ al-Fataawa (24/269).
It says in Fataawa al-Lajnah ad-Daa’imah (21/404): I was pregnant, in my ninth month, and I felt some pains for which I had to go to the hospital. The specialist doctor advised me to have emergency surgery to save the baby, as it was not possible to give birth in the natural manner, but I refused to have that surgery. The doctor advised me that if I did not agree to having this emergency surgery, that would pose a danger to the foetus, and might cause the foetus to die. In fact the foetus died in my womb a few days later.
Is there any sin on me for that, and should I regard myself as having caused the death of the foetus, because of my refusal to have the surgery that would have saved the life of the foetus which was in danger, by Allah’s will, according to the advice of the doctors? Does this mean I must offer expiation, by fasting for two consecutive months?
Answer: If the situation is as mentioned in the question, then there is no blame on you for the death of the foetus, because the fact that you refused to have the surgery is not regarded as negligence regarding thelife of the foetus or as a cause of its death.
Moreover, the surgery may not have achieved the intended goal mentioned by the doctor. The basic principle is that one is not liable, praise be to Allah.
And Allah is the source of strength. May Allah send blessings and peace upon our Prophet Muhammad and his family and companions. End quote.
To sum up, you do not have to do anything.
And Allah knows best.