12 is an odd age, she may enjoy some silly games at a party. The Guides haloween party used to be full of silly games like pin the spider on the web, the closest to the middle gets a sweetie. We decorated cupcakes with black icing, silver balls for eyes and fizzy strawberry laces trimmed up for spiders legs. Apple bobbing and eatibg a doughnut off a paper plate without usibg your hands was fun. Chocolate bar game, big bar of dairy milk (or cheaper alternative) gloves, hat, scarf ( or mittens if you are cruel) a dice and a knife and fork. Sit in a circle with choc on a tray or something flat and firm with cutlery, hat, scarf, gloves nearby, if tgey roll a six get to pit on hat, scarf and gloves and cut a cube off, one cube at a time and eat before eating the next one, meamwhhile tge rest are tgrowing the dice to get a six, next who does has to put on scarf, hat and gloves and pick up where the last one was.
A night of silly games with her friends might be nice and they could involve DD. Maybe later in the evening, you and your mum do somethibg special with her, I am not keen on the paper ballons that are powered by flame as I see the unpleasant consequences that happen when they finally land. Does Aunty have a favourite spot (beach or view) you could go for a walk earlier in the day and share memories.
It's hard at that age to show emotion at a party that is meantvyo be fun.
Lost my cousin when her girls were 12, 10 and 6 and my Gran took tgem under her wing, birthdays are hard and emotional, but they like family contact to share emotion, it's hard witg friends, puttibg on a brave face etc.