If your wife started investing in May, the SP 500 was around 2100 and had high valuations for several months before the market started to dip. If a 4% drop in value (-$200) is making you nervous, I would highly suggest you reevaluate your risk tolerance and your asset allocation.
On a separate note, see if your wife can shift away from AXA. They have VERY expensive funds with high fees and hidden costs. AXA is by far the most aggressive 403b provider I have encountered and do very well with getting individuals to invest in their accounts without reading about the costs. Your wife should definitely call her district HR office to see if there are other 403b providers such as fidelity or vanguard, which offer much less expensive funds.