Question about the "offer call

So, I got it. Five interviews, one skills test, around two-month process—I got the call today. Position offered. I accepted. I'm having a bit of a dispute with my sister about this, though. She thinks

So, I got it. Five interviews, one skills test, around two-month process—I got the call today. Position offered. I accepted. I'm having a bit of a dispute with my sister about this, though. She thinks I shouldn't have verbally accepted the job. My sister (a CEO, by the way) thinks I should have said, "I'd like to see the offer letter with everything written down before I formally accept." She said I gave away my bargaining power for things like salary and equity and signing bonuses. However: - They offered me the exact salary I requested, which was only $2,000 below their max salary listed in the job description's salary range. So I'm not exactly sure what there is to negotiate there..? - The benefits sound great. Health insurance is a 90% employer-paid benefit. What is there to negotiate there? - It's a nonprofit, so there aren't any stock options or equity to negotiate there. - It's basically an entry-level editorial position. So, a signing bonus would have been an absurd ask, I feel. - The start date was fine with me. I accepted during the call because I've been unemployed for ages and the job offer was exactly what I wanted. What is there to play hardball about? Am I wrong here? It sucks because I'm really excited about this job, and she was the first person I told, and her first reaction was to roll her eyes at the fact that I accepted it over the phone. She made me feel like an idiot. So, I guess I'm wondering if I am an idiot. -- UPDATE: Thank you everyone for your advice and kind words. I decided to go with my gut and the general consensus here and leave it alone. I didn't let the organization catch wind of this internal conflict, and I certainly didn't renegotiate. They sent a written offer the day after this call. Most everything we discussed verbally was reflected in the letter, so I did ask for one or two things to be added, which they did happily. I signed it, locked this down with no issues, and I'm starting in the new year!! Thanks again!