Dear tomz,
i had been charting my temps for 8 months and still couldn't tell when I ovulated because it was so eratic. The last month I have been testing with ovulation prediction strips and finally identified an exact day - between 12 to 36 hours - when I ovulate. It turns out that I ovulated about 1 week after the doctors told me it usually occurs, day 14, or there abouts. For me, the strips were the only way to tell. They are not very expensive, I bought 100 of them for aussie$35 and began testing on day 14 of my cycle - once a day until the lh surge had been detected.
I would recommend the ovulation strips for your wife, or anybody getting frustrated with charting as they are a certainty, unlike temperatures, which can be hard to analyse. Further, this puts less strain on the partnership if the lady is wanting to have sex every night in case she ovulates. With the strips, you know when the time is right and you can enjoy yourselves instead of making it a routine, which is exactly what I almost forced upon my partner. Some nights were fun, others felt like hard work.
Anyway, this is a long-winded way of saying "try the strips" and best of luck.
Shaman