I find SD12 increasingly unpleasant

I hear what you’re saying but her behaviour is getting worse (in my opinion) and I’m finding it increasingly hard to be around.

Some examples:

1. She messages DH and my family members asking for money. When they say no, she’ll ignore them
2. whenever DH and I disagree, even on something minor like what to make for dinner, she has to insert herself into the conversation to tell me I’m wrong and he’s right
3. She hounds DH for attention to the extent that the others don’t get a look in. If they sit next to him, she’ll sit on his lap. I can’t even hold his hand without her intervening. Yet when she’s at her mum’s, she leaves him on read
4. We sometimes have family movie nights (no pressure if you’d rather read or be in your room instead). If she hasn’t picked the film, she’ll talk through it until it’s ruined for everyone
5. If she gets told off, she cries and is melodramatic until she’s getting comfort and attention. The reason she was told off is forgotten about

I’ve tried to build bonds with her and she’s not interested unless it’s something that means me spending lots of money and excludes her siblings. If I suggest something like cinema with her, she’ll openly say she’d rather have the cash, or that I should take her siblings instead (so she can be with her dad).

The girl doesn’t want to go out with OP unless OP spends big money on her! What do you want OP to do, force her?

This exactly. I find myself increasingly shocked by these responses. Truly truly shocked.

Also.. who says “ghastly”.. who are you Enid Blyton?

No destroying her by playing favourites with her siblings and disengageing/grey rocking her.
This is causing the behaviour and creating a destructive environment for that poor child, who deserves better from the adults in her life.
This woman is creating a golden child/black sheep narrative and environment ho spend some time on the relationship board and talk to the survivors of such environments and then come back and tell me that this woman isn't destroying this poor child

Destroying a child by not giving into her demands for expensive treats all the time?

Now I've heard it all.

I assume you are married to the dad and yuu live with these kids at least some of the time. (Just checking as people use the term "step" sometimes when they aren't married).

If this is the case, I think it behoves you to try to have as positive a relationship as you can with this kid. Whatever your secret thoughts, you need to conceal the fact that you don't actually like her.

… And I don’t know what I can do about it.

I’ve known these kids for eight years. I’ve always gelled with SD13 (sweet, creative, slightly awkward) and SS9 (funny, sporty, loving). SD12 has always been the one I’ve had the least in common with. She’s extroverted, dominant and wants to have her own way.

AIBU: I should make more of an effort to bond with her
AINBU: it’s okay not to like everyone, just remain polite and keep distance when possible

I hear what you’re saying but her behaviour is getting worse (in my opinion) and I’m finding it increasingly hard to be around.

Some examples:

1. She messages DH and my family members asking for money. When they say no, she’ll ignore them
2. whenever DH and I disagree, even on something minor like what to make for dinner, she has to insert herself into the conversation to tell me I’m wrong and he’s right
3. She hounds DH for attention to the extent that the others don’t get a look in. If they sit next to him, she’ll sit on his lap. I can’t even hold his hand without her intervening. Yet when she’s at her mum’s, she leaves him on read
4. We sometimes have family movie nights (no pressure if you’d rather read or be in your room instead). If she hasn’t picked the film, she’ll talk through it until it’s ruined for everyone
5. If she gets told off, she cries and is melodramatic until she’s getting comfort and attention. The reason she was told off is forgotten about

I’ve tried to build bonds with her and she’s not interested unless it’s something that means me spending lots of money and excludes her siblings. If I suggest something like cinema with her, she’ll openly say she’d rather have the cash, or that I should take her siblings instead (so she can be with her dad).

Outrageous? You must live a very sheltered, highly controlled life!

Yes it is behaviour that needs to be corrected by a parent - but it’s not outrageous- she isn’t torturing small animals or telling wild lies to social services.

That is achild who is screaming out about her unhappiness and one who is picking up your animosity towards her.
You need to treat all 3 children the same regardless of how you feel about them if you can't then you need to leave her dad asap.
The fact that you think its acceptable or appropriate to gray rock a 12 year old because you haven't gelled with her, whilst still being close to her siblings proves that you shouldn't be a stepmother and is most likely the cause of her behaviour.
I really don't understand how you can think that its acceptable to create a black sheep and treat her differently than her siblings because quite frankly its disgusting behaviour from you.
You are destroying this poor child all because you dont like her she's 12 ffs be a decent person and leave before you do anymore damage with your favouritism and exclusionary attitude and behaviour

I hear what you’re saying but her behaviour is getting worse (in my opinion) and I’m finding it increasingly hard to be around.

Some examples:

1. She messages DH and my family members asking for money. When they say no, she’ll ignore them
2. whenever DH and I disagree, even on something minor like what to make for dinner, she has to insert herself into the conversation to tell me I’m wrong and he’s right
3. She hounds DH for attention to the extent that the others don’t get a look in. If they sit next to him, she’ll sit on his lap. I can’t even hold his hand without her intervening. Yet when she’s at her mum’s, she leaves him on read
4. We sometimes have family movie nights (no pressure if you’d rather read or be in your room instead). If she hasn’t picked the film, she’ll talk through it until it’s ruined for everyone
5. If she gets told off, she cries and is melodramatic until she’s getting comfort and attention. The reason she was told off is forgotten about

I’ve tried to build bonds with her and she’s not interested unless it’s something that means me spending lots of money and excludes her siblings. If I suggest something like cinema with her, she’ll openly say she’d rather have the cash, or that I should take her siblings instead (so she can be with her dad).

I hear what you’re saying but her behaviour is getting worse (in my opinion) and I’m finding it increasingly hard to be around.

Some examples:

1. She messages DH and my family members asking for money. When they say no, she’ll ignore them
2. whenever DH and I disagree, even on something minor like what to make for dinner, she has to insert herself into the conversation to tell me I’m wrong and he’s right
3. She hounds DH for attention to the extent that the others don’t get a look in. If they sit next to him, she’ll sit on his lap. I can’t even hold his hand without her intervening. Yet when she’s at her mum’s, she leaves him on read
4. We sometimes have family movie nights (no pressure if you’d rather read or be in your room instead). If she hasn’t picked the film, she’ll talk through it until it’s ruined for everyone
5. If she gets told off, she cries and is melodramatic until she’s getting comfort and attention. The reason she was told off is forgotten about

I’ve tried to build bonds with her and she’s not interested unless it’s something that means me spending lots of money and excludes her siblings. If I suggest something like cinema with her, she’ll openly say she’d rather have the cash, or that I should take her siblings instead (so she can be with her dad).