I guess this must be quite common in some families as it was certainly the case in ours. In the end we stopped visiting my DM every year. She lived a nearly 400 miles away, but moved in retirement after DDad died. It was such a long way to go only to find that other GC were always treated more favourably.
It always came across that DM felt sorry for Dsis and felt that I could take care of myself and had better job and a less shit DH. She lived near to Dsis and was aware of everything which happened in her life, whereas she saw my life at long distance through rose tinted glasses and I did not enlighten her.
As young adults my DC are well aware of the family dynamics and DS often says I have to think "would you really want to be in Dsis's shoes? If the answer is no, just move on and get over it".
My Dsis always muscled in on the act if we planned any activities on what was actually a family holiday we had paid good money for, including accommodation. The last time this happened our DC were adults, we all went out for a walk and then a meal, which was actually suggested by Grandma. When it came time to pay the bill, Dsis sat tight and didn't offer anything towards the cost. It appeared that she was quite used to DM picking up the tab on her behalf. My DM did not have enough cash to pay even half the bill for seven people (she still thinks of things in 1970s prices). I picked up the tab for all of us, to save her any embarrassment. DM is in her late eighties and lives on a pension, so has to be careful. Dsis has a job and their home is bigger/worth more than ours, but her husband spends a lot of time and money in the pub. It must affect her disposable income.
As DCs were adults by that time, they had a great laugh about it afterwards and it has become a family joke, with Dsis as the CF. Nonetheless, they are aware of always being second best. This is how it will be for your DD if you let it continue.
Telling them that DD feels pushed out and asking them directly to see her on her own is one option. If you arrive and the other GC is there leave after a very short time and say politely you will come back when they are less busy. They might get the message and they might not. Sad to say, but you cannot change the family dynamics by just putting up with it.