She had some secretions in which there was a thread of blood

Praise be to Allah.

Menses is the well-known bleeding, as the Prophet (blessings and peace of Allah be upon him) said to Faatimah bint Abi Hubaysh: “The blood of menses is dark and recognizable. When it is like that, then refrain from praying, and when it is otherwise, then do wudoo’ and pray.” Narrated by an-Nasaa’i (216); classed as saheeh by al-Albaani in Saheeh Sunan an-Nasaa’i.

Menses has signs which are well known to women. With regard to the colour, it is black or dark red; with regard to the smell, it has an unpleasant order. It is also thick; it is blood that flows from the uterus, so it cannot be one or two drops, and it cannot be like a thread.

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: If a woman has a few spots of blood during the day of Ramadan, and this continues with her throughout the month of Ramadan, and she continues to fast, is her fast valid?

He replied: Yes, her fast is valid. As for these few spots, they do not mean anything, because they come from a vein.

It was narrated from ‘Ali ibn Abi Taalib (may Allah be pleased with him) that he said: These spots, if they are like the blood from a nosebleed, they are not menses. This is how it was narrated from him, may Allah be pleased with him. End quote from 60 Su’aalan fi’l-Hayd, p. 6.

Based on that, what you emitted is not regarded as menses, and you must fast.

And Allah knows best.