If they were invested in doing it properly they would give her her own supporting cast, but I doubt that is what they are doing.
Compare this OC to other new-ish Batfamily characters such as Duke Thomas and Harper Row.
Unique Mantle: Duke = yes, Harper = yes, Ryan = no.
Unique Superhero Costume: Duke = yes, Harper = yes, Ryan = no.
Comes with own supporting cast (usually family members): Duke = yes, Harper = yes, Ryan = no.
Okay, this one is still up for debate, but there haven't been any new (permanent) cast announcements thusfar.
Directly replaces an existing character: Duke = no, Harper = no, Ryan = yes.
The new OC is supposed to be "nothing like Kate Kane", but uses her mantle, has her family as supporting cast, practically has the same suit, will probably use her bike and so on and so forth. Oh, and the showrunners are basically re-doing season 1. New vigilante comes in to replace missing hero, but has to prove themselves capable, huh. Season 1, Batman goes missing, Kate becomes Batwoman and all the struggles that involves. Season 2, Batwoman goes missing and...oh, I see.
So I'm going to assume that Kate found Bruce, and whatever he's been up to is more fun than being in the Arrowverse, so Kate joined him.