Any support or experiences with extreme stranger anxiety / separation anxiety?

My daughter has just turned 8 months old. Ever since she was a few weeks old, she has hated anyone other than me or her dad holding her. She cries and cries until she's handed back to one of us. Given her current age we know it's probably separation anxiety, but that doesn't account for the fact she was doing this at 4 months old which is before separation anxiety kicks in.

If she's left in a room with anyone other than us, it's the same story with the crying, whether people are at a distance and not touching her or on the floor trying to play with her. She has seen her grandparents once per week almost all her life, they are so supportive and it's really getting me down that they can't hold her or even really interact with her without her crying. I've made extra trips to stay over at my parents to try to help her get used to them - no progress. Since my baby was 9 weeks old we've gone to 2 different baby groups per week - so it's not like she doesn't ever see other people. She enjoys these groups too.

This situation also means that my relationship with my husband has suffered as we can't do anything just us 2 as if we leave the baby with anyone she just screams and screams.

In 8 weeks my daughter starts nursery, I can't see how she's going to cope - trying to trust the process that nursery will have seen it all before.

I know people will say this is very normal - but it's not usual that grandparents have only really managed to hold her as a newborn as at every point past the newborn stage she's just cried.

Any advice or experiences welcome!