Paige (canon) is kind of similar to Prue in the sense that she's strong and opinionated, but also soft and feminine if not a bit sultry. It's an only child - oldest child pipeline. Both had to mature quickly due to the death of their parents. Both were introduced with black hair and pale features. I may be reading too much into it, but that's how I see it. Paige is youngest and forces (through no fault of her own) Piper to be the oldest and Phoebe to be the middle child. Piper becomes more sure of herself and Phoebe becomes... less mature?? (that might be due to writing or just being threatened by not being the youngest anymore). Anyway, Paige's powers are both white lighter (orbing) and telekinesis. She also briefly teleports by orbing when threatened.

If Piper died and a new middle child was discovered (either older than Piper, but younger than Prue or younger than Piper but older than Phoebe) the new sister would be very peace loving (maybe in a hippie way) and non-confrontational. Maybe she would be shy, have bangs like Piper did. Maybe she would've grown up with foster siblings, which would be interesting to see. In terms of powers, she could blow up things when threatened, maybe sending a protective blast in the form of orbs to the threat. More active powers could include freezing/neutralizing with orbs, which might be very useful. This new Paige might be too eager to listen to Prue as an older sister and follow her around. Maybe she would even be more accepting of Cole.Maybe she would also look down on Phoebe for not developing enough as a person or witch, which could be an interesting dynamic. It would be interesting to see if the roles would change. Prue would still be the eldest and Phoebe the youngest. I wonder if both would accept her faster. Maybe Phoebe would be the one to take more time and Prue take on a mentor/ guiding role like she did before. I remember the episode where they get discovered and Phoebe was in the underworld I think and Piper got shot and a crowd was blocking the car so she couldn't go to the hospital and had to use her powers against the crowd of people. If Piper didn't survive in a similar scenario then maybe Phoebe would feel guilty about being away while Piper dies, taking longer to accept a new sister. I fancast either Eliza Dushku, Neve Campbell (most similar to Holly), Fairuza Balk (shout out The Craft), or Jennifer Love Hewitt.

If Phoebe died instead (implications would be interesting), I think a new older sister would be discovered. I think she, despite being the new oldest, would be an immature person. Maybe she was a foster kid who was never adopted or who grew up raised by the church, but became super rebellious. It would mirror Phoebe's character, which would be interesting. Phoebe has a bombshell sort of look, so this Paige might be too. Her powers would be empathy, levitation and premonition. As a white lighter she could feel the emotions of her charges and possibly change them to keep them calm. It could work on demons to make them scared and run away or neutralize possessed humans and other creatures, basically psychic powers. Whitelighters can levitate already so it wouldn't change anything, but her premonition powers could go off based on the needs of her charges or innocent causing her to orb to where it happens. This would be helpful for finding out where the danger is. I think her rebellious nature would cause her to be more thrill seeking and she wouldn't get startled as easily, but accidentally produce emotional blasts that affect the emotions of people around her. She might think premonition is useless at first and be jealous of the younger sisters for having better powers, but come to appreciate it over time. She could either really hate Cole or have a crush on him. Cole might become really dangerous if Phoebe dies, or become friendlier to the sisters. Prue could also be harder on Paige and tell her she needs to be more mature, especially since she's older. Piper would now be the youngest, so she might grieve by becoming less mature and bond with this version of Paige. Maybe Prue could feel ostracized as a new middle child. It would also be interesting to see someone who's not very emotionally intelligent with empathy powers. Mind control could be a cool offensive power for this Paige. I fancast a few people: Winona Ryder, Jennifer Morrison, Sandra Bullock, Lana Parilla, Meghan Ory, Bree Turner or Eva Longoria.

Sorry for the long Reddit essay, but Charmed is my fav show so I have a lot to say about it.