Strictly speaking, BA are within their rights to do this. However, it does seem very unfair if the delays were caused by problems at ORD.

Sounds to me like your wife got an unhelpful ticket agent on a bad day. I would have expected BA to be more sympathetic - in the past when I've missed a connecting flight because my first flight was delayed in taking off, BA were quite happy to just put me on the next flight out - no fuss, no charge.