Overwatch coins vs credits

Certain skins on my game cost 1000 credits, while they cost 1000 overwatch coins for my sister (for the same skins). I don’t understand why this is? I’m playing on PS5, while she is playing on PS4.

I tried to include links to the images but it wouldn’t let me.

I assume it you’re an old ow1 player and she a new player?

I think she played ow1 for about 40 minutes , but she doesn’t have all the heros unlocked in ow2. She has the origin edition skins unlocked though without purchasing anything in ow2. She also has a random reaper skin unlocked from the shop?? Like I said she hasn’t purchased anything in ow2 so we are confused where it came from.

Does she have enough credits to unlock the 1000 skin with? It could default to coins if not. Or have you two tried to unlock the skin at all?
It should ask what currency you want to use if it’s possible to use credits on the skin in question.