Friendship - trials and tribulations

Here's the situation:

About a month ago we agreed to go out to dinner tonight with some friends - to an Indian restaurant 15 miles away.
In the meantime, last week we got the keys to our new house. The house was a bombsite - the last owners left a multitude of junk in all the rooms which we have had to dispose of, and about 12 years worth of dust and grime. I have spent all week scrubbing, hauling, polishing, steaming, vacuuming.... all whilst looking after my 15 month old baby girl. When it got too hard on her I called in the grannies to help - which unfortunately has thrown out her routine and she has become unable to settle herself to sleep at night, something which she has never had a problem with before.
RC, my lovely hubby has been unable to get time off work, and as he is working 12 hour shifts this week - he hasn't even seen the house yet.
Yesterday all my belongings arrived from NZ. I was at the house from 7am till 6pm and I am only half way done unpacking.
Tonight will be the first night we spend in the house together. It may take a while to get my little girl to settle to sleep, and to top it all my car has broke down and won't be ready till Monday.
RC is working till 8 again. We can either get a taxi there and back (££££) or his lovely daddy has offered to drive 20 miles to collect us and take us to the restaurant - a 40 mile round trip for him. RC is then up for work again at 7.

So, everthing is telling me to cancel. It makes sense to cancel. We will be falling asleep at the dinner table. And I really just want to curl up on the sofa in front of the TV.

So why am I stressing about it?
My friend will sulk. She won't understand. She'll just tell me to leave Maya with her granny - that she'll be fine.
And I will feel guilty.

I'm letting no one down - there were going to be 6 of us going, so there will still be 4.

Oh dear. It surely shouldn't be this hard. It's times like these that I wish I was in NZ - slightly different culture/mentality about this type of thing.

Bite the bullet, kiwi, just do it.