Assalamu alaikum ustadh. If a woman experiences some unusual discharges (light yellow) at times and after performing many prayers she notices this. Is it mandatory for her to check before every Salah and are her Salah invalid cause she was negligent!

What is mandatory is that if shee sees this and you are certain then this nullifies the wudhu so she makes wudhu and prays, but I am afraid that you are falling into waswas and this is something we don't want, therefore the answer is general not detailed also there are many details for this.