Hi there
Good information already! Definitley speak to insurance Brokers, as they'll have access to policies not normally offered on all the price comparison sites.
Overall, yes it does matter you've had no claims or points of any kind, yes it does matter how long you've had your full UK license as well. Seeing as you'd had it less than a year, you are in the highest risk catagory. One good aspect is that you're a girl and you will be seen as less of a risk than a boy!
Some companies and underwriters will take into account that you've had a long previous driving record in the US with no claims or accidents etc. However, they will counter that the US driving experience isn't applicable to the UK as we are different here - Right hand drive and Drive on the Left etc - However it's worth a go and any reduction is a good thing. Finding which ones do offer some concession is hard though as theres so many underwriters and insurance companies. Have a look through this site as this questions pops up quite often and I'm sure I've read some people have written in and got some reductions.
Jennbean - I'm sure you mean 'Adrian Flux' insurance! ?!
Cheers, DtM! West London & Slough UK!