First off, when it gets to GRUB, is it a prompt? Try typing DOS when you get there and see what it does.
Second, am I understanding correctly that you have windows on one hard drive and Linux on the other? During the install, where did you select to have GRUB put? I have always had a dual boot system, and have always put it on the MBR without any problems at all. I compared my grub.conf file with the one you posted and don't see anything really out of the ordinary.
Third: what about your BIOS settings, where is it set to boot from?
Fourth: For a quick fix, so your mom could get back into windows, you could try the old fdisk /mbr trick explained here
Although, with that option, you'll have to boot into Linux with your boot disk and reinstall GRUB onto the MBR later and mess with it until you can get it to work.
Anyway, there are some suggestions...