I'm so very sorry you have had to deal with the deadly fallout from this balloon release. It's so dreadfully pointless and I can't help but wonder where, exactly, people who organise these events imagine the detritus will end up? Even if it didn't pose such a risk to livestock and wildlife, at the very least, it creates unsightly litter - at no small expense either.
I'm not immune to grief, and the completely natural desire to remember someone who's died but there are numerous alternatives for doing this in a positive way, such as making charitable donations, or, as others have already mentioned, creating new life by way of planting trees (or sponsoring organisations who do this) or wildlife flower seeding in suitable locations. How lovely if you remember your loved one by gestures like this. Even the memorial bench is a welcome rest point and the plaque ensures their name isn't forgotten.
Balloons, and lanterns too, strike me I'm afraid as very selfish photo opportunities more than anything else. They float away - God knows where - and that's it, gone to be someone else's time consuming, costly and/or heartbreaking problem. It's wanton destruction. Do pretty pictures to look back upon really assuage grief? Do they provide genuine comfort? IME, very little actually does in the early stages of losing someone, whatever you do, and therefore doing something so deadly for the environment is especially pointless. And for anyone who claims that they do, well, tough, they come at too high a price for others.
I wouldn't be involved in this and would have no hesitation in telling the bereaved parties why - gently, at first, as it may be ignorance of the effects but I wouldn't mince words if necessary. This doesn't mean I'd be unsympathetic to their loss but I couldn't condone behaviour which results in even more loss.