Hi. I am a childminder and would NEVER leave my ds (2.6) or mindees of that age with an 8 month old. The number of children is fine (I have my own ds and 2 other toddlers) as you are allowed up to 3 under 5's however I'm very surprised she left those ages all together. I know from my ds and the mindees I have that children of 2/3 have lots of energy and wouldn't know how careful they would need to be with a younger baby. Even if they are so good that they do know to be careful, I would not be happy about them being able to pick a younger child up like that. I've never gone in a different room to do contracts but am not saying this is really bad. I do however think she should have let you have your baby with you as 8 months is too young to be left alone (my own ds started crawling at 6 months and 1 day old and was into EVERYTHING so I'd say best to be with an adult at all times!!!
As for Fennels comment 'And you expect a childminder to be more cautious than a parent not less. I suspect the childminder isn't being careful enough.' - I totally agree. I don't neglect my own ds (promise!!) but I feel a duty to watch other people's children even more carefully!
I'm sorry to say that I'd go with my gut feeling.
Hope you sort something out!
As for the charges for holidays, I'm afraid that is quite normal as she'd loose a lot of income otherwise. If you want term time only care, I'd contact your local CIS for a list of childminders who offer this.