Exactly notanan. That was the point I was making (albeit , not very succinctly). It's a 50-50 thing. And quick scan of Mumsnet shows how many young mums feel steam-rollered by MILs (mostly, but Mums are guilty too ). I am loathe to use the words ' it was different in our day' but my mum completely kept her distance and had to be persuaded to have DD1 (4 years old) in an emergency for 3 nights. She made it very clear when we picked DD up that it was not going to be a regular thing.
My advice, for what it's worth, to newbie Grans, is hold fire, wait to be asked, and if it doesn't suit your plans, apologise (very gently) while making sure you leave the door open for being asked again.
. If it's a genuine immergency fair enough but I'm afraid if it's a 'date night', hen partiy, or spa weekend...... hire a professional!