What to do about getting married in a month?

Okay, I (22m) asked my high school sweetheart (22f) to marry me last year. Little back story I vaped and hid it from her for a while. She found out she forgave me. Told her I quit (I did not) and it was back and forth on that for a year or so. I finally quit. I mean I told her to leave me that I was a liar and everything else. I didn’t say that to make her feel bad or anything. But, she stayed with me. We grew together, got better together, we were inseparable. We did everything together before I asked her to marry me. And if we wanted to do anything with friends or anything we could and no body would get mad.

Okay, she’s got a job now. Which another back story, my parents bought her a car to go to school, paid for half of her school, (she worked and paid for the rest of it).

Anyways, we get engaged she treats my sister (8) like crap. Before the engagement she was so nice to her, did her hair, painted her nails, everything. Now she doesn’t hardly talk to my parents, doesn’t want me hanging out with my friends or anything. She’s currently mad at me because I have hung out with friends, when she was invited but she didn’t want to come. My sister was with us the past couple nights and we had a blast.

She currently won’t talk to me. She gets mad at me over the littlest things, won’t help my parents with anything, even if it’s the slightest thing. I bend over backwards for her I’m there at her beckoned. She acts snobby towards people, she doesn’t talk to people unless she likes them ( we are a very popular family around here). I have 25k into this wedding that my fiancée and me have funded into this wedding. I don’t know if she thinks we are wealthy, or if I’ve done something, or anything. Anytime I try to talk about this to her she just gets mad and says I’m taking up for my parents. Also she cries sometimes and says “she’s gonna miss her mommy”

I do know weddings are stressful. But it’s been like this since she’s gotten the ring. I know I’m not perfect, I know when you get married you leave your parents and cling to your spouse. I don’t know what happened. How can I talk to her? How can I be a better man to help her? How can I talk to her without her getting irate at me?

Thanks to all that say something.