I have found a cake on the web which is a sponge with ground almonds and a layer of crushed amaretti biscuits and raspberries in it. It keeps a couple of days so should be good. We will have five hours of driving, plus the tunnel so I don't want to leave anything to do when I get there. DD can buy the cream and the candles!
A seven year old might not appreciate a pavlova with cream, if it doesn't look like her idea of a birthday cake. Sponge layers and raspberries thickened to a spreadable jam or compote can be assembled into a layer cake, covered in icing and decorated when you get there. She could help to decorate it, too.
Rasperry Summer Pudding - then it won't matter if the raspberries are gooey/soft. No cooking and you've only got to transport the rasperries - easy-peasy.
I like the jelly and rum baba idea as OH has been wanting to make that since the first round of Bake Off. She would like the raspberry jelly as we made that together when she was here in the summer. Might have to substitute the rum though! I am not sure that she is that keen on meringue and I do need somewhere to stick the candles..
I am thinking that you could set the rasberries in a thicker than usual, made up raspberry jelly, transport in tupperware, chop up and pile in meringue/flan/rumbaba.
Meringue. Make layers in advance, pack between greasproof paper, put in tin. Always assuming your grandaughter likes meringue. Open or layered Pavlova with the raspberries any other fruit she loves. OR Layered shortbead with lashings of cream and raspberries. OR Do individual knickerbocker glories.
Both more puddings than cakes - but hey - no real difference.
We need to make a birthday cake for our grandaughter who will be seven in a couple of weeks. She loves raspberries and I have got plenty of this year's crop in the freezer, so that is fine. We need to make it a couple of days in advance, so we can take it to England with us. I don't think she would be that keen on chocolate or coffee. Any ideas? We can add cream and decorations when we get there.