$300 for just the board? Board and bindings? Or board, bindings, boots, socks, pants, jacket, etc.?
They can get a pretty nice board for $300. Board and bindings are possible if you can find last year's gear or get really lucky on this year's (I got my gf this year's Arbor Eden with last year's Rome Madisons for $310.) But if they need everything, their only option is used gear.
If they go with used, I'd recommend spending the bulk of their money on new boots. That's the most important gear to get a perfect fit. And if they keep at it, they'll be able to use them for a few years with better gear. For a board, I'd check ebay and craigslist for some of lilfoot's suggestions. She probably knows more about women's gear than anyone else on here. You'll probably find better deals on boards and bindings together. Ebay should be fine for jackets and pants too. Most girls I know go through jackets faster than they have a chance to go out of style.