OP I have been in the same situation as your cousins where I have had no close family or support. It can be so so hard.
What I did was anytime I could help people I would. Also in the UK there are many people in the same boat so sometimes it helps to know you can try find a different support network.
I always try to help people by offering play dates, baby sitting and on and on. That way it can be swings and roundabouts.
Also when I was really ill I didn't feel bad about endless takeaways (it was the only way my children could eat at night for a whole) and so on it just had to be done as I couldn't even cook or go upstairs.
Thankfully a single mum took my kids and dropped them to and back from school, she did this before and after I go out of hospital, she just came up to me one day and said you look so Ill let me do drop off and pick up.
There was another mum who worked full time and took my children on a play date for two weekends in a row. Those two Saturdays allowed me a 3 hour break whist the time was massive for me.
I always think that at such a crap time in my life to see someone helping me selflessly really made me feel better.
So now I really do go out of my way to help.
Your cousins should not worry and I hope she can ask for help.