Well, we didn't speak to her last night as dh came home and said that his colleague (who she had been helping out as a second job) didn't want her to help anymore, so I didn't think it fair to hit her with a double-whammy! Anyway, I've now emailed her and asked her if she would like to finish earlier since without the second job, she is likely to get very bored just doing the hours we need her to do.
Feeling less p*ssed off about the lie, although still not super happy, but I'd still rather she left earlier and maybe there is some element of me looking for a reason to ask her to go. We're not that happy with her general performance and it has got worse in the last couple of weeks. For example, when she first started looking after our ds, she cooked him a proper meal for his dinner; last Monday, he got bread and jam for dinner which I would not have thought anyone could really consider a healthy meal for a toddler! Plus, I got home a bit early one night last week and heard her through an open window speaking to him very sharply which made me wonder how she usually dealt with him in our absence. So you see, there really are a lot of other things going on in the background and I can see how if you look at this incident in isolation - which is how I wrote the OP - it might look unreasonable.
I agree that a 27 year old is very different to a 19 year old, but because ds was 9 mo when she started, we wanted someone who was more mature. But I would also expect somebody who was older to let me know if she did not like any of our rules. The funny thing is that I copied the house rules from another MN thread and that was the only reason they included a rule that she couldn't stay away overnight unless agreed (or whatever it said - can't remember exactly now). I would never have thought of it myself, but could see that it had its advantages from an employers' point of view!
Blueshoes - thanks
Scottishthistle - the new nanny is live-out. She is also 27 and has her own daughter who comes to work with her. I like the idea that ds will have another child to play with until his baby brother/sister arrives! I agree 100% that living out is so, so much easier.
Mud - you are correct that it is not recommended for an au pair to look after a child under 3 for long periods of time, but when we took her on holiday with us at Christmas, we could see that she was very patient and competent with ds and the fact she was that bit older meant we were happy that she was capable of being entrused with his care. Also, she had been with us 5 months by the time she started looking after ds on Mondays.
Pointydog - I say "in loco parentis" because it is a common phrase. I am only 5 years older than her so am clearly not in a parental position, but I do feel responsible for her as the person who brought her into this country... The first time she went up to London for a weekend, I was extremely nervous for her as her English was virtually non-existant - we didn't realise how bad until she arrived! London is big place and she couldn't even have asked directions to a train station if she got lost. Obviously, after a couple of trips, we were happy that she could find her own way around and her English has improved no end as a result of having an English boyfriend.
Marathon post... If you're still reading - thanks for bothering and well done for getting to the end!