Father sponsoring Mother's B2 visa

My father got his B2 visa in 2017 and he self sponsored it. My mother got her passport made recently and is applying for B2 visa now, and they both plan to travel together. I have put my father as her sponsor in DS 160. What documents would she need to produce? Is it sufficient to have a letter from my father stating he will sponsor along with his passport, visa and bank FD statements? Does he need to fill out the i134 sponsorship form?

Yes, that’s about it. Usually, the funds requirement is the key one, if your father is a sponsor. He does not need to fill it out. It is optional. You can also send your invite letter and status documents as backup for reference. Check Parents Visa Documents Checklist USA