Praise be to Allah.
What is meant by secretions from the vagina is secretions that come from the uterus. These secretions are colourless and a woman may not be aware of them coming out. They vary and may be lighter for one woman and heavier for another.
In al-Mawsoo‘ah al-Fiqhiyyah (32/85) it says: Secretions from the vagina are a colourless liquid that may be madhiy or sweat. End quote.
Ibn Hazm (may Allah be pleased with him) was of the view that these secretions do not invalidate wudoo’.
However the majority are of the view that they do invalidate wudoo’, unless they are continuous, in which case she should do wudoo’ for every prayer after the time for it begins, after which it will not matter if any secretion comes out.
See the answer to question no. 44980
According to the opinion that it invalidates wudoo’, it is not obligatory to do wudoo’ for that unless one is certain that it has come out. If there is any doubt as to whether what has come out is secretions or sweat, it is not obligatory to do wudoo’, because the basic principle is that one remains in a state of purity unless one is certain that what invalidates it has occurred.
And Allah knows best.