I'm pleased that you aren't keeping her on - she's not a good fit for you and she isn't making your life easier - which is one of the main reasons to have a nanny and not a cheaper childcare option.
It doesn't sound, from what you have said, that you need a nanny to be that flexible really, just stay later occasionally or change what she is doing on employed days. There are plenty of nanny jobs out there that require a much greater degree of flexibility.
Little things like swapping the playdate over can be a little annoying if the parent changes their working days often as you don't feel like you know where you're at - however, although it's a little frustrating, you'd still rearrange the playdate and accomodate the parent rather than yourself/other nanny.
There's no way you should have suggested or she should have allowed you to be doing the housework, while she ran a playdate. I personally think it's better to have a nanny and a cleaner - but I can see why you have done what you have done and if she agreed to that, then it shouldn't be an issue.
I don't think there is any problem with you 'letting' her do the ironing at her house or being flexible with the hours etc there aren't any hard & fast rules to how it 'should be' - however it needs to work for both of you and this is only working for her.
Don't worry about her 'blacklisting' you, either her 'nanny friends' know what she's like and although they might be friends with her, they quite possibly wouldn't employ her themselves! and as has been mentioned - they already have jobs. Nanny jobs are a bit thin on the ground right now, so you will find someone else easily.
Don't feel bad, this is what trial periods are for :)