Dan,
Things to look for: all metal gears, a motor overload/reset button or feature.
I also prefer the bowl lift design to the head tilt design. I just think it's a sturdier design. You can get pretty good deals on 5 qt "professional" grade KA mixers. These have 475 watt motors and all-steel gears. The second is important because lesser KA mixers might have plastic gears that can strip out and then cost a small fortune to replace. Apparently in some cases they would strip out just mixing bread dough. The ones with metal gears should also have a "reset" feature, either on the speed control or a separate reset button. This is important to protect the motor in case the mixer jams on something. Instead of burning out the motor, or stripping the gears, the reset feature will sense a motor overload and stop the power to the motor.
I've been seeing the 5 qt professional model at Costco for about $260. That's a very good price for such a powerful and versatile mixer. And it comes in some pretty nice colors. The matte finish platinum is particularly fine. You might also want to look into getting her an accessory set - which operates off the power takeoff on the front of the mixer, and which may include a shredder/slicer, a meat grinder, a pasta maker. Other nice accessories might include a grain mill, a juicer (citrus type), a food mill.
Of course, if your mom prefers the tilt-head, by all means go with that. The tilt-heads are generally less powerful, with less capacity, and have lower prices as well (although I've seen stores like Macy's carry everyday prices for tilt-heads that are more than what Costco charges for a bowl-lift model!