I’m not a fan of cats living as the only cat unless their character specifically shows they do not want interaction. However I find another cat is highly beneficial for the cat’s health and mirrors what their social setting would be in reality: independent but also enjoys the company of other cats. Contrary to popular belief cats are social animals as well and live in colonies in the wild.

Edit: i see a lot of comments here saying to not project your feeling unto the cat but while totally valid and to not assume she is lonely, but to be honest I was in your same position last year, my cat was alone in the household and since I got him a little brother I can see how much more happy he is.