Anyone remember a book by Jean Ure about 2 girls called Laura & Lisa who fell out over a pen! From the 80s.?

I think it may have been called 'Best Friends', but can't find it listed on any of Jean Ure's bibliographies. If I remember correctly it is one of the 'Woodside School' series and the cl were going on a trip and everyone was into pens that had their initials dangling off them and Laura managed to buy the one with 'L' first and she fell out with her best friend. Strange request, I know, but its driving me mad since me and my friend were reminiscing about our school days! Thanks