2 Car Seats?

Natasha
Hey ladies! So I'm really confused and needed some help. My daughter will be 13 months by the time the second baby comes around  in November. Originally we thought we could use her car seat for the next one and put her in a booster. But then we realized boosters can't be used until the child is 3-4 years old is that right? Our daughter is almost reaching the maximum height for her current car seat so what does she move into next if not a booster? Any suggestions would be great. Thank you!! 
Edit: thank you all so much for your input, we are looking into getting her a convertible car seat and will definitely keep her rear facing till 18 months.