Well first of all, it's Catherine with a C, which will help your internet search a little.
The two main publishers of large print titles are Ulverscroft -
http://www.ulverscroft.com/ and W F Howes -
http://www.wfhowes.co.uk/ . The title isn't listed on either website, but they're bringing new stuff out all the time so it might be worth giving them a call, especially as the original wasn't published until last year.
For your information, both companies publish monthly lists of their titles. It may be worth asking them to put your mother on the mailing list. They also produce audiobooks, which she might like to consider as well.