Yes you can use the present SIM in another device
As to another SIM cheapest way is to look at comparison websites. Often there are special deals on there. I'm paying £8 for something that costs £20 with O2 direct.
Whatever you choose remember that all networks are about to increase their prices by inflation plus 3.9% around April, so factor that in to your calculations.
If your daughter uses a lot of Social Media look at Voxi which is run by Vodafone. Data used by many Social media apps does not count for data usage.
This is not O2 and we are all customers here similar to yourself and cannot answer account type queries.
