Overclocking your "computer" (read: CPU/RAM) or videocard (GPU and/or RAM) does not increase your run speed in FFXI
My ancient athlon xp 2500+ is running at 3200+ speeds (2200mhz), and I have my system ram running at CAS2.5 (default CAS 3), and my character runs at default speed
there's something else wrong with her computer, obviously
to me it sounds like a chipset problem, an actual hardware problem on her end that probably needs to be replaced (maybe the CPU was partially damaged by a power surge, or maybe her PSU is causing the CPU to get too much voltage, or the motherboard may have a physical defect somewhere)
but purposely overclocking your system does not give you any speed enhancements, that's a fact