I haven't RTFT so apologies if this has all been said.
At this age (9) most children, and especially girls, have so many insecurities. In our society it comes with the territory! For you (and us) one of them is being' poor' compared to those around us. For those who are financially better off, their insecurities will be just as valid but may not be money related. If we can help our children understand and be aware of this, it makes the whole 'awakening to life outside the family bubble' much easier.
We had a very similar thing with our DD and it started around the same age. We live in an area that is a good mix socioeconomically, however it would be considered an affluent area on the whole.
The primary school was very small and most were very well off families living in huge houses. She became very aware of the differences. Asking why we were 'poor' (we're not) etc. It was quite intense for about a year and then became less and less of a focus (she seemed a little obsessed for a few months.).
I just made sure that I engaged with her and didn't rubbish her feelings and views. I was very age appropriately honest with her. My view is that if our children are asking the question, they are ready for an honest answer as possible.
We would give her examples of everything she had. All the travel and holidays, school trips. Her own room, great parties, all her clubs and out of school activities. We also made her look around and acknowledge actual poverty and what it really looks like and why it is not important from the perspective she was giving it. She definitely became more aware of 'real' life. She also began to see that well off/rich has minimal bearing on happiness. And her friends always love coming to our house and tell her how lucky she is to get on so well with her parents.
Once sleepovers and spending time in other households became more frequent as she got older, she realised that we are not poor and, even if we had been, her home life and relationship with us and our wider family, is more open, happy and healthy than those of lots of her friend (her observation from frank discussions with friends) .
An upside is that she is determined to do well, give herself the best start as possible and work at being financially independent - she studies really hard and has recently started her first regular paid job (only 8 hours per week but earns enough to enjoy and join in with her friends).
The insecurity of being less well off resurfaced again recently (she's at 6th form college) - again, part of a very affluent group of friends and has her first serious BF whose family is rich. She's become aware of how run down our little terraced home is. It hasn't helped that my job was made redundant last summer due to pandemic.
This time around though, she's much more realistic about what our economic status means in the grand scheme of things. She even said she doesn't want any presents for her birthday and would prefer it going towards home improvements. Of course, that's not going to happen and I told her this. If our financial status is an issue with her friends/BF, I pointed out that she probably should get new friends/BF. And she's admitted it's not their problem, it's her own. She's embarrassed that it may reflect negatively on her but doesn't know why she feels this way. I don't either and we agreed it's something only she can work out.
It's hard living in a world that constantly tells us the important things in life are material and celebrity is so revered - and these 'role models' (!) only become celebrities to sell stuff and ideals to young impressionable children! It's very different to our childhoods. Our children are bombarded 24/7 despite our best efforts to shield them from all the noise and unrealistic crap. All we can do is listen and acknowledge their feelings, fears and worries, discuss them honestly and they will grow out of them.
Good luck