Hi Miriam,
There are a couple of options that would be possibilities - apologies as I don't know where the parish boundaries start and stop but in order of walking distance the closest ones to 10 Duke Street appear to be:
St Mungo's RC Church in Townhead (10 Duke St is a few minutes walk closer to St Mungos that St Alphonsus);
St Alphonsus RC Church, Stevenson St
St Mary's RC Church, Abercromby St
Our Lady of Good Counsel, Craigpark (this is a newer 1960s church, but may have replaced an earlier one)
St Andrew's RC Cathedral in Clyde Street
If she was living in Stockwell Street at the time of her Confirmation, I think the Cathedral would be the closest.
Not sure if that helps, but might narrow your options.
Best wishes
Rockford