It's entirely your decision and if you're comfortable then go for it.
I'm in a strange position in that I would totally trust my MIL to look after Earl overnight but she lives 4 hours away so we stay over too.She is a nurse and has soooo much experience with children and she respects us as parents! She has offered to look after him over night so we get a full night's sleep but when he was 10 days old (last time we were there) I wasn't ready to relinquish him. Now, with him 2 months old, I would probably jump at the chance (we're meant to be going in Feb so maybe then).
My Mum on the other hand I really wouldn't trust her. There are a lot of issues there, but there is one thing, she is on anti-depressants and can't handle pressure.....so how could she cope with him in the middle of the night when even I will admit he can be a handful (he's not good when sleepy.....just like Mummy and Daddy!). My step-dad has one hell of a temper(I know from experience) and I don't like the thought of something happening. They don't listen to me about what to feed my dog when they visit so how can I trust them not to give Earl something he shouldn't have? My Mum has a habit of not putting him down too....and he's not good if he gets too hot, and she's always got 4 jumpers on due to bad circulation ....it all adds up to NOOOOOOOOOO! lol
I think if you have a good relationship with her then I don't see why not as baby has to get used to people, and different ways of doing things. If it doesn't go well then you could maybe wait a while until you try again, but if nothing else you would get a break!
