One of my friends is a step mother to two adults for 25 years.
She is so kind but had many many years of PA from her step daughter.
Her step son has always been lovely and accepting of her, they are close.
She couldn't have children and accepted it and moved on.
She was always very firmly held at a distance and accepted it completely, her husband was largely on the fence as there was no overt rudeness, just PA that she was not HER mother etc, which she never claimed to be anyway.
However, when this step daughter married and became pregnant she was very quick to allocate childcare between her now retired step mother and MIL, via her father!
Her own mother has a busy full-time career and has clearly stated she was unavailable.
MIL agreed max two days and she wanted 3 from my friend.
My friend had worked as a teacher for 30 years, received a nice inheritance and promptly retired early, and had zero interest in being tied down.
She communicated to her husband that he was welcome to be involved but she would not be tied down, having finally retired too.
Her husband expected her to come around as she is so kind, by the end of the mat leave.
He was wrong.
She had polite interest in his grandchild and is kind, but no huge interest.
She took to making arrangements the night before to go out with friends and would stay over and not be around the next morning for the first few weeks, to reinforce her position.
She stayed with me a few times.
Her husband very quickly got very snappy with her as the little girl is very full on and the three days were long.
My friend booked a visit to her sister in Australia for 6 weeks as she was both upset and pissed off at her husband attitude and that he wasn't respectful of her right to not want to be free childcare for his daughter.
He was VERY surprised at the trip and she gave him a few home truths before she left.
By the time she returned his grandchild was with a childminder as it was just too much for him🤨.
The past two years have been interesting.
Her husband is a lot more wary of her as he has seen her steel.
Funnily enough she has a much better relationship with her step daughter who has a lot more wary respect for her too.
Her mother has little time for a grandchild, her MIL has other grandchildren, so I think having had her own child she has seen a bit more clearly the kindness my friend has shown her consistently over the past 25 years.
She has helped out a couple of times when SD has been very stuck and has finally gotten some real appreciation from her.
If my friend had been excluded from the wedding and her husband hadn't stood by her, I could imagine it would have been marriage ending.
If the OP is now realising that grandparent involvement would be welcome and handy, she has rightly messed up.
She can't have it both ways.