Voluntarily. I have 3 children. A 24 year old boy who lives with his mom. A 22 year old daughter who lives with me and a 18 year old now at uni. When the children were younger I was pay 25% of may salary, then it was 20% and now it is 15%. I earn around £400 net per week.
You can stop paying the mother immediately.
Your daughter has a potential claim against you if she can show that her income from all sources does not meet her reasonable needs - but she would not get as much as you are currently paying her mother
I hope that this is of assistance - please ask if you need further details