Hi
"Northlands" which is situated on North Road, Cardiff and is now a residential care home for the Elderly (I think it's Salvation Army run) was once a home for mothers and babies.
I'm not sure if this was the case during 1922, but certainly during the 1950s and 60s it was a home for unmarried mothers. During that time I believe that most of the babies born there were adopted.
I think you should consider the possibility that the reason your grandmother came to Cardiff from Ireland was due to a pregnancy, although as I wrote above I'm by no means certain that Northlands was a mother and baby home in 1922, it may have just been a young person hostel.
Hope this helps
Regards
Caro