Our nanny has worked for us for around 2 months. She is part time. Since she started there have been signs that she is struggling a bit with money. One of these being she asked us if we would be willing to provide her with a rather large personal loan.
Very recently she said if I needed her for any extra hours, she would be happy to help - so we agreed days and hours for this month. At the weekend I sent her a quick message just to make sure she remembered the extra hours this week. She replied saying yes all booked in, however she now felt that financially, it wasn't worth her while and said I either needed to pay her cash in hand or a higher hourly rate. I agreed that evening babysitting work could be paid cash in hand and she replied to saying that's absolutely great etc etc. Only for her to then text me today with a really weak excuse pulling out of the agreed extra hours this week!! It felt very obviously a lie, so I suggested I was disappointed at being let down last minute and I asked her if we needed to sit down and have a chat. I said I was worried that perhaps the job isn't working out for her financially. She has since text back with another bizarre explanation saying she can now do all the extra hours again. 
She doesn't have any financial problems and she is very happy in her job !!
I am genuinely a bit confused by what is going on. I feel upset that she is willing to lie to me. I really feel being a nanny is an important position of trust and if she is willing to lie so blatantly, what else would she lie about. However do you think that is an overreaction. She's quite young, is this just a sign of immaturity - she doesn't want to do the work but isn't able to have an honest discussion with me. AIBU to be upset? How should I tackle this now??