Now with the AMD she'll get future 64-bit support, should she ever need it. But with the MXM I should be able to upgrade the video card for her should she ever need to. Also, Intel MIGHT release 64-bit Pentium M on the same chipset, maybe :/
Intel isn't adding 64-bit extensions to the Pentium M until well into 2006, possibly 2007.
The next Pentium M core, Yonah, is going to bump it up to Dual Core, add Intel's Virtualization technology, a 666Mhz bus, SSE3, and a few new power management options.
So, if she's not going to play games, go with the 64-Bit AMD.