I'm a child from a blended family and tbh, the only problem is that which you are making of it.
Your dd will just take as natural whatever you act as being natural. If you just behave like it is completely normal for people to refer to her as having half siblings, being a step GC etc. then she won't be bothered by this at all.
You are lucky that they treat her kindly. She is not being pushed out, they may be doing things for your ds that they haven't done for her (well, she wasn't on the scene when she was 7mo, was she), but she had a granny who did things for her which she isn't going to be around to do for your ds.
It's just the way things are, and if you behave like things are natural and are happy that they are kind and loving to your dd, she will feel the same, if you seethe with resentment for whatever they are not doing that you feel she should be entitled to, she will do the same, and be worse off for it.
I have step sibs, half sibs, step parents galore, have had step gps and the whole lot.
In some things we have been treated the same, in some things we haven't. Overall my half sibs have received a load more than me (the other half of their family are rich!), but because I actually feel that the other side owed me nothing at all I consider myself fortunate that I did receive quite a lot from them.
If I felt entitled to equality I would be quite bitter, which would be ridiculous given that I have been given loads. So what if others got more? Lucky them!