My friend had the exact same problem as you, so you are not alone.
My friend fought long and hard to get funding from the LA for a 1-1 support worker for her son, at school.
Same thing happened, and the teacher started to use the support worker as an unofficial TA for other children.
My friend really had to put her foot down and complain, as it was affecting her son.
Listening to my friend, this is my advice.
Do not feel guilty.
Yes, there are problems with support in schools and yes, teachers need more support. But that isn't your fight.
You are your daughters advocate and you have clearly fought long and hard for this funding.
Unfortunately, as you are now seeing, you also need to keep fighting to keep it and make sure others dont take advantage of it.
My friend said to me that she understands the frustration that other children dont get the same support and she is more than happy to help other parents to get the funding for their children.
But, she will not be sharing hers sons funding.