It's more likely that the chipset on the motherboard is the culprit. As far as processors go, stick with Intel, but I don't think that's your mom's problem.
My guess would be that she has a VIA based chipset. I made the mistake of buying a board with that brand of chipset and am sure I never will make that mistake again. It seems odd that a salesman would be interested in saving your mother some money, doesn't it?
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351W 89 Mustang GT Convertible