Zero need for a girls specific bike, well unless she is in the habit of wearing long flowing dresses
My daughter is tall and a confident rider, and when she reached that age, it was time for a lime green (her request) Frog 73, which she has only just grown out of at the age of 12, it lasted her a good while.
I would offer it, but we are a long way from Leeds.
I have found all of mine on Facebook Marketplace or one of the Frog/Isla/kids bike selling pages.
I'd suggest either a Frog 69 or 73, both 26" wheel bikes iirc, and she'll have a bit of growing room, but it won't be enormous to start.
Is she confident, and able to stop/start over the cross bar, or does she need to be able to get both her feet flat down whilst sat in the saddle?
If the latter, then definitely go smaller.
Having just had a very quick search on FB marketplace for Frog City Bike, or Frog girls bike, nothing came up matching your picture, and I must be honest, I didn't know they even existed.
Either it's very new, or they don't really sell any, as I suspect most buyers will want a gender generic bike that either will be happy to ride, and can be passed onto siblings, and or sell on easily.
Having said that, IF you can find one, perhaps it will be excellent value, due to less demand.
Winstanleys have them new for £399, and
Decathlon at £427.
*You almost certainly are aware, but the Frog bike you pictured will be pretty light (maybe ~9-10kg) and designed for smaller hands etc, but there will be a LOT of bike shaped objects out there, with a step through frame at an apparently reasonable price, but they will weigh as much as a small house - which will do her no favours at all.
