http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=390x2693The lady who sold me my first serger said, "Sewing machines have personalities, sergers have attitudes"
You don't want to go cheap. 4-thread sergers will serve her well.
Good brands, Juki, Babylock, Janome. Cadillac$$$$: Husky, Bernina (and they are excellent machines)
I'll put it like this: you will get what you pay for. The higher end models offer training. I got training with my machine and it was the best thing.
Caution when buying a used one -- sergers that are damaged may also have timing damage - a big thing when it comes to making it work.
Also get her some extra needles made for her machine. Sergers have attitudes about bent or damaged needles. I am conservative, change them out after every project. (but then, my serger has lasted about 15 years, still works)