Relative only acknowledging one child.

[Cheeseaandbiscuits]

DP and I had two children, DS(2yo) DD(newborn). DP also has adult daughter (I will refer to as DSD for sake of post but I don't have a relationship with her).

When DS was born DSD nose was very out of joint and took nothing to do with him, basically didn't acknowledge and when she did it was fairly nasty. She since has had quite a distant and strained relationship with DP.

DD was born little over a month ago and her attitude has been very different. She sent two gifts, one clearly for a baby and one which could be for a baby or toddler. More I think about it I think they were both aimed at DD. Over past few weeks she's showed a lot of interest and has been texting asking about children, or so I though.
It's now quite clear to me that she's over ever been asking about DD and still isn't really acknowledging DS.

Any advice? DP is so pleased she's now having some involvement I think he may have rose tinted glasses on and don't see what she's doing, I know I need to tread very carefully with what I say because it is his daughter. Although anything I say he'd deny on her behalf and insist it's not the case.
I was happy to give her a chance but no way am I allowing her to hurt my son like that (he's too young to understand now but it won't always be the case)

Take it at face value.

Assume positive intent (one last time until you observe otherwise).

Give her a chance to be nice and loving to your DCs - it might be awkward at first,

You are right to be cautious given her previous behaviours - but if she has turned over a new leaf this could be a lovely experience for both your DCs and your DH.

I think it sounds like she wants to do the right thing, after, perhaps understandably, behaving immaturely in the past, and the new baby has given her a pretext to try to build bridges. To me there's not enough evidence from what you have said to think she's going to favour the youngest one in the longer term. The current focus on a new baby is almost inevitable.

I would encourage her attempts to bond. It could enrich the lives of your DC and DP. And your own life too, in the fullness of time.

I sense that you are looking for reasons not to like your step daughter? Do you see her as a threat to your little family that you have created with your partner? Sometimes I feel really sorry for older children from first relationships as they just get pushed aside. I bet you'll want her cut out of the Will next

“I would encourage her attempts to bond. It could enrich the lives of your DC and DP. And your own life too, in the fullness of time.”

This. You haven’t described any behaviour from her which sounds obviously ill-intentioned, just a bit thoughtless which I think is quite normal for a young adult out in the world. Time flies. Her twenties are likely to be the most footloose and fancy free period of her life and she naturally has other priorities. That doesn’t make her a bad person.

You have chosen a partner who already has a child and even though she was an adult when you got together, I think it’s important you behave in a way which allows her to feel welcome in your family rather than harbouring resentment and dislike, which is what you appear to be doing. Imagine your own DCs in her shoes 20 years from now. How would you feel if someone else was attributing negative motives to them in the way you are with your DSD? Imagine if someone was trying to drive a wedge between them and you the way your thinking seems likely to drive a wedge between your DP and your DSD. This is an opportunity to welcome her into the fold. Why not just embrace it?

You might be being oversensitive. Don't read too much into it - accept the gift, mention both children, and leave the door open for more contact/acknowledgement from her over time.

There is really no need to be this suspicious of other people. You dont need to second guess every little thing. Just leave the door open, and deal with things as they come up. It will probably be fine. And even if it isnt, nothing is permanent, babies grownup, young adults pair off and have their own babies... really there is unlikely to be a hill worth dying on in your case...