Just ask her for her number as she would give to anyone who already lives in London. The number she gives you is the number you dial.

Most London numbers start with 020 followed by either 7 or 8.
So if your friend gave you 0208******* as a number [asteriks represent the numbers] that is what you would dial. You do not need to add +44 as you would if you were outside of the UK.

To be honest, I don’t understand the confusion but I hope my answer gave you some clarification.

Well, you obviously don’t need to dial the country code, because you’re in the country already.

However, you should probably dial the city (area) code. Without knowing which airport you arrive in it’s impossible to tell, but both Gatwick and Stansted are well outside the area for London codes.

One thing, though: the area code always begins with a 0 when dialled within the country, which is left off when dialled internationally. So if you have a number in the form +44 20 8888 8888 you should add a 0: 020 8888 8888.

Just the city code. You’d only ever need to use the country code (+44) if you were outwith the UK.