Does signing into account with different ID affect Whatsapp data?

Hey, my Mum has an Iphone and there is currently no ID signed in - TBH, I don't know who was last signed in (she lives in another country and is getting older, so its a lost cause on getting the right info from her). Could have been a friend's account(?)

She has been using the phone for years now but now needs to update some apps to continue using them e.g. Whatsapp, Messenger, etc..

My plan is to create her own apple ID and then get her to sign in using that new ID. What i'm trying to avoid, and what she is worried about, is losing any messages/data from the Whatsapp account when the ID signs in and updates the apps. She doesn't really use any other apps of interest, so if some disappear and need downloaded again that's fine but she has pictures, messages, etc.. in Whatsapp and messenger she doesn't want to lose.

In my mind it shouldn't lose it as its linked to her MSISDN/SIM, which will still be in the phone, but i've never tried it before.

I've read some articles but they don't definitively say yes/no on whether data is lost or not. Has anyone actually done this and can comment on what happens?

Thanks in advance :)