A very difficult situation shodg and I understand your feelings. Has your DH said how he feels about meeting up with his D?
If he's happy to do so, he may get some answers to some of your questions, for example why she's waited so long and depending on how this goes, it may help to put some of your concerns regarding her motives to rest.
As a first step meeting, try to be as supportive and understanding as you can and see what transpires. If more meetings are suggested that you will also be excluded from, that would be the time IMO to tell your DH how you feel.
You say you have a 33 year old son so have been together a long time. It may be necessary for his D to be reminded that you come as a pair and perhaps be made aware that any future relationship she has with her father will include you as his wife and mother to his son.