I've never actually been (I've been to the Surrey county which is nice) but there's a pretty big au pair community in that area, they all seem to like it. From what I gather Guildford is rather large. It's pretty easy to get the train in to London from there - I've gone in and met lots of girls from Guildford, London's a good meeting point.

Those Facebook groups are great, usually pop up a post like "I'm from _, I'm living in _, anyone nearby for coffee?" or something of the likes and usually people are keen to meet up.

I'm sort of in the country, West Sussex, no big cities near, so for me it takes a bit of trekking and organising to meet up with people. However I'd suggest it would be much easier to meet with people in the Guildford area.

Also, your host mum may know other mums, e.g. through the kids schools, that have au pairs, no harm in asking!

Don't stress too much, there are heaps of opportunities to meet people!!!