Since I have never been to the US, I do not know what is considered a decent cash gift at a wedding, and that too for a close relative such a niece. Does $2500-3000 sound decent? Thanks in advance! What is considered a decent cash gift at a wedding for a niece?

My sister is 32 and been with her fiancé over 10 years. She got engaged at 31. By 27 my sister wanted to be engaged but her boyfriend never saved or tried moving out. I've been with my boyfriend for a year and a half. He's moving out wants me to join him. My sister said it would be "selfish" if I got engaged by in the next year or so because my parents will need time to financially recuperate after her wedding. She said, "He'll never have a ring by then anyway he could never save that quickly after moving out." This is the usual antics my sister does when she feels insecure or envious. She told me I'd never get into my masters program. Then when I did finish with honors, she told me the starting salary is terrible like 40k, though I left making 75k. Yet it was okay when I watched her drive luxury cars, go on 2-3 vacations a year. I watched her decorate an apartment all while I budgeted an paid off student loans. The moment she senses I its a special moment for me, she sulks and removes herself. She always comes from a place of competition and envy. She's worried we'll be engaged at the same time or I'll get my ring sooner than she did. It's not "stealing thunder" when I'll be 28. It definitely is not far-fetched that at 28 and with a great career and relationship that I'd want my personal life to progress too. Does anyone have a sister like this? Sometimes it's just exhausting.