Council Tax Challenge Comparison Advice

Klare1

I'm trying to help an elderly neighbour to decide if she should challenge her CT Band.  She is in Band C and the second part of Martin's pre challenge check is easy, the 1991 value suggests an A or B. She lives in a 2 up 2 down terrace.
It's the first part I'm struggling with, comparing like for like. Our Street is full of individual properties, no two houses are the same and are a mix of old (victorian or older) or newer properties from the 60's-80's. There are also a few grand old houses on the street which have been converted into flats. And a couple of very Grand houses that are Banded at G.  
There are a total of 47 listings on GOV.UK for our street but 12 have been deleted. We live in a high tourist area so the majority of the smaller properties are deleted on Gov.uk as they will be Airbnb businesses. 

Should I use the wider area to try and gather evidence of similar? How far distance wise would you go, as again I fear many smaller will be deleted.

Thanks in advance 

lincroft1710

Go for terraced similar aged 2 bed in a slightly wider area, try 0.5 mile radius to start with