auntie or just my name?

I have an older half sister, she's 37, I'm 31.

I always very much looked up to her and we've both had rough childhoods. Different but still rough. Where her mom was abusing alcohol (She's been clean now for a very long time, more than a decade) my mother really wanted me to be a boy and she had a boy after me. I was very much abused both emotionally and physically. My mother though she didn't physically abuse me allowed it to happen and to this day still will deny it ever happened.

Our dad isn't bad but he's a bit of a know it all and his current partner hasn't been kind to either of us at all. My dad says she really regrets it but actions really do show something else. She appreciates that I try to keep family ties.. but I don't really know how deep that goes. I'm still uncomfortable around her.

Anyways both of us, my sister and I, don't really have those strong family ties as people sometimes have.

My sister tends to back out of every family thing on our side of the family so we don't really have a lot of contact. Even though she does tend to invite my dad and his partner, we are rarely invited.

Well tomorrow me and my son are invited to an event regarding her daughter.. Which is a thing because she didn't actually invite me, My dad asked me if I was invited and when I told him no, he said he was going to force the issue by bringing up to her a carpooling arrangement..

So later she sent the invitation to a family chat saying she sent it to the wrong chatgroup.. idk.. It'd be spectacular if she actually INTENDED to invite us.

But I'm going. My son and I picked out a gift and I'm writing a card..

I just don't know if I should write "auntie *my name*" or just "*my name*" & name of my kid.

I don't think the kid truly knows I'm her aunt. We've seen eachother maybe 10 times.. My niece is 7yo.. We did go on a weekend trip together last year to celebrate my dad's anniversary (which was really uncomfortable for both me and my sister)