Ok, there will be spoilers for Steins Gate 0 so be sure to watch that before reading this post or just read the overall part.
In Beta timeline Kurisu is dead. The Beta timeline is the timeline we start to watch. Okabe goes to the Alpha timeline where Kurisu still lives. The Alpha timeline is where Mayuri destined to die. This is also the timeline we see the most in OG Steins Gate. All the experiment on D-Mail, stuff like changing the gender of Ruka, done in this timeline and get reverted by Okabe in order to save Mayuri.
In the end, Okabe understands that there is no way to keep Mayuri alive in the Alpha timeline. He goes back to the Beta timeline in order to save Kurisu. He fails once and this is the start of Steins Gate 0. In S;G0 Okabe chooses to stay in this timeline and keep Mayuri save by sacrificing Kurisu so Kurisu is still dead in this timeline. We also saw a small segment in the middle of S;G0 where another version of Okabe chose Kurisu over Mayuri. That is the Alpha line.
- The alpha timeline is where Kurisu lives and Mayuri dies.
- The beta timeline is where Kurisu dies and Mayuri lives.
Because of two distinct timelines, there are actually two different versions of Suzuha.