Look bro, The glass is a metaphor for your home and the water is tension. You can easily lift 500 times the amount of water in a glass for a short time but if you hold 4 oz of water for a long time, you can get tired. Same with tension in a household.
We are just regular people with our own shortfalls and only are looking at your situation through the lenses you have provided so most people will think that you’re wife is being childish, petty, etc but that’s your perspective as well. Yes, we all need understanding and I know that this situation is difficult for you. You cannot understand her and she appears very petty to you “making mountains out of molehills” but the truth is that you and she come from different backgrounds and have different needs. That doesn’t mean, one person is more correct or their needs are more important.
The thing about marriage is that it is difficult until you learn to truly live together. Your wife left her home and those who love her the most and is now living with not just one stranger but two in an environment that seems utterly differnent to say the least. She is not getting emotionally, whatever it is she needs to feel loved, secure, and safe.
Your SIL has been in your family for 10 years and she is very comfortable with your Mom, you, and the rest of the family. And she may have been like that from the beginning. Everyone has different needs.
Talks are good but follow them up with actions. Do something nice for your wife on a consistent basis. Something to invest your future. You can do a weekend getaway once a quarter or you can sit with her and watch her favorite show every evening or do dikr with her or read a book every night for 10 minutes on how to understand each other better.
Remember, consistency and keep remembering that she’s the love of your life and your humsafar (your travel partner in this journey).