Is it obligatory to repeat the ablution if a clear liquid is found in the nose after ablution, and it is not known whether it came out before or after washing the face?

The questioner's intrusive thoughts should be answered by ignoring them. What she described as a transparent fluid from the nose is not a barrier that prevents water from reaching the skin; rather, it is a form of intrusive thought (waswasah), and her ablution (wudu') is valid. The criterion for a barrier is that it must have a tangible mass that prevents water from reaching [the skin]. If a barrier is found after ablution and it is probable that it appeared subsequently, then it should be considered as having appeared afterward.