My mom often lends money to my cousins and they usually don't pay her back. My mom feels guilty she has money and they don't and wants to help. I think she's not helping but enabling. I've pointed out that she's enabling and she's agreed with me and then continues to do it, getting defensive and frustrated when I bring it up again. She doesn't even keep track of what they have borrowed and paid back. The amounts of money range from $1500 to $10,000. My mom has also paid for multiple trips for these cousins- sometimes out of generosity, sometimes because they booked them and then couldn't pay for everything afterwards. I think my mom is setting up my cousins for a lifetime of bad financial decisions, and I think my cousins don't see a need to change bad spending habits because my mom will always bail them out. I don't even know if it's really my place to say or do anything, but I worry anyway.
What a tough situation to be in. You see your mother being financially taken advantage of, and nothing you have done so far has helped. Addressing the issue with her was the right move, however, it appears that while she intellectually agrees with you, she doesn't feel like she is doing the right thing by withholding money from your cousins.
Enabling behavior is confusing to those outside of it. While you and I can see that your mother is removing the natural consequences from your cousins' actions (thereby allowing them to develop unhealthy and unsustainable spending patterns), your mother's guilt and desire to help them appears to be clouding her judgment. She probably doesn't think what they are doing is good, but is caught up in the short term desire to make them (and herself!) feel good. She also probably feels the pressure of not wanting them to get in trouble (missing out on a vacation they planned, but couldn't afford).
Your best chance is to see if she will see a licensed psychotherapist about this issue. This is an issue that can take a while to unpack and figure out why she feels like she needs to help them in this way. You can also ask your mother how she would feel if you were doing what she is doing. It might help her to think about her actions from an outside perspective.
If nothing works, then step back and let her experience the consequences of her action. Let her experience having less extra money, trouble paying her own bills, and hurting her relationship with her cousins. And be there for her if and when she decides to make a change.