That is not good for your mind and sanity feeling stuck. And it's partly why orders are there to be enforced if they're not working. Court is also about resolving issues and reaching solutions and courts like people to try and reach reasonable agreements if possible and in an environment at court that is encouraged to happen. Also the court can assess for themselves what they think the Mother's attitude was.
The problem is if trying to decide what to do and getting distressed leads you to having problems coping, it does mean something needs to be done. Since you started giving the jiffy bags (great idea) it seems your ex is pushing back harder. Your daughter is rejecting you. Yes they could explain it away with anxiety over Mum grieving and losing grandma and the timing etc, and possible get a solution in place which the Mother is on board with - temporarily if they think that. But alarm bells should ring if a 5 year old child is rejecting a parent and showing hate or anger.
Obviously the SW has scared you a bit about the idea of going back to court. But you need a solution. What are you supposed to do - just go away? The other reason I think it needs to go back to court is - if you do nothing, it is as if you have accepted the changed arrangements and you went through all that to get an order for nothing and it end up being a worthless piece of paper.
If it was me I would send the letter before action, giving the Mother the opportunity to make it happen and if it doesn;t on the next occasion, put the enforcement application in so the courts are aware their order is not being followed. At least then, even if the order is varied and supervised is extended a bit longer - you are not in breach of an order yourself. Sadly if no action is taken with breaches it becomes accepted as agreement and the order is changed. You can make suggestions and proposals and solutions in your court application and sound reasonable.
Some of the things you overheard your ex saying are outrageous - I am not sure if you're maybe just feelign sorry for her due to the bereavement. But your priority is ensuring your child doesn't lose a relationship with you.
At times like this - no decision leads to a downward spiral of stress, self doubt and uncertainty. So sometimes any decision is better than none. A decision to ask the court to try and help resolve the matter, or a decision to do nothing - while being fully aware of the consequences of doing nothing.
There is a middle ground - which I think you have tried already. Your ex has the power to keep your daughter at home. The only power you have is someone more important than your ex telling her what she must