If it's the Irish dependant allowance it is means tested on the wife's income. That doesn't stop the wife buying extra UK years, but she would have to do the sums, and see if receiving the UK pension would put her over the threshold, and if so, which would be more financially beneficial. It may be possible for her to receive a small UK pension and still qualify as a dependant here.
It's not the same situation, but my husband received a dependant allowance for me (means tested) with his partial UK pension, while I continued to buy extra UK pension years myself, working up from 7 to 20. I thought his pension would fall when I reached pension age and started receiving my own UK state pension, but somehow as I had more qualifying years than he did, he actually benefitted!