If your spouse is just starting out in racing Tri and is not going to be going into it on a regular basis then I'd suggest a used bike too.

Check out the local bike clubs, they often have classified ads in their newsletters or web sites. $300 isn't much for a decent bike that she can keep for a long time, but again as others have stated, better to get a bike that fits. And I don't mean just your typical fit session in a low-end store where they have you stand over the top tube and see if there is space between you and the frame - there is more involved to it than that. You may want to get a different stem (take-offs at bike shops have lots of those) that works.

Also get your wife involved in the buying decision and fitting.

Good luck.