Backstory: I've been with my OH for coming up to 8 years, known SDs since they were 18 mths and nearly 4. They know us as "daddy and icy" and in many ways it's been an easier ride as they don't have the Disney memories of parents together and the dream that if only the wicked stepmonster l would just fuck off their family would be a unit again. That's never been an issue, and I'm grateful.
We have a good relationship, in the main, older SD periods started here and she's very comfortable telling me when she started (I'd sorted pads etc out a few mths ago and we'd had a "practice"), she'll say when she's on etc.
I'm now pregnant (after a traumatic few years of trying and ivf/FET etc). The younger SD is very excited and keen. The older is much more taciturn about it, which is her way generally. I'm not trying to force any sort of "family" thing on them - beyond maybe making it a bit of a family-team effort - all of us vs the baby, and taking about future-stuff, so how when older SD is older it would be cool as she can drive her little sibling to parties etc, so that it's a 'concept' rather than an expectation.
Anyway, older SD hasn't always been VERY jealous. When they were little, she'd have anything her sister wanted, couldn't share, catchphrase was "MINE". She's displaying some jealousy re the baby already - by going back to her mum's and making comments - which are then fed back in such a way that I can only presume the intention to make OH feel guilty.
I don't know what to do now. I'm irritated enough that I'd love to list out all the stuff I do for her, pay for with my own money, arrange for her, am planning to do for her and say all that can bloody stop. That's clearly NOT a helpful option, so I'll keep my fantasy bollockings to myself! BUT should I address the jealousy/sharing concerns on the basis "you're nearly 12 now, so let's think about how the age gap will work and how you want to approach this as it's a change" or just leave her to do/think/bitch to her mum talk to her mum and address it as and when?
How best not to fuck her up basically, whilst not putting her at the centre of histrionics (which may or may not be exacerbated by exW)?!
Thanks & sorry for long post.