Okay so I dyed my hair to a dark brown color but there is still some blonde patches coming through my mom wants to dye it again but we aren't sure if you can dye it twice in one day so if someone could please tell me if you can or not that would be great and by the way the hair color I used was garnier so tell me something

Make sure that you use the same color and brand of dye and only color the patchy areas. If you re-do your entire head you could end up with hair darker than you originally wanted. Dye areas that didn't get dyed only and you should be okay.

Yes. There's no chemical reason that you can't. Your scalp may not appreciate it.