What is the ruling on one from whom semen is discharged while she is performing ghusl for menstruation and cannot stop it? Should she complete the ghusl for menstruation while the discharge of semen continues?

We fear that what you mention is waswas (whispering from Satan). If you are certain that what is discharged from you is manī (spermatic fluid), then its discharge does not invalidate the ghusl (ritual bath). However, you must perform ghusl after its discharge stops, if it was accompanied by pleasure. Some scholars hold that ghusl is obligatory even if it is discharged without pleasure. If its discharge is continuous (sals al-manī - chronic spermatic discharge), you should perform ghusl for each prayer as a precaution, and wudu' (ablution) for each prayer will suffice you. However, if they are normal discharges, they do not invalidate the ghusl, and you must perform wudu' after their discharge stops. If their discharge is continuous (sals al-ifrazat - chronic vaginal discharge), you perform wudu' for each prayer after its time has begun.