Of course you should allow your daughter's friends to come round to play and vice versa
and on another note as a mum and nana my self I always found it advantageous to be friendly with the other mums and dads while waiting for my children to come out of school. Not all children tell their parents everything that goes on in school (I remember well conversations like 'what did you do in school today....'nothing;' would come the reply) Not every little incident is reported to a parent eg one child spitting on another.....and yes it does happen. I now work in a school at dinner time in the playground and know for a fact that not all, not even much, of what goes on there gets back to the parent via the teacher who was told of incidents by a dinner lady, like me, so please, YES YES YES get to know your daughter's friends and also their parents....
hope I haven't bored you with all that but I happen to think that it is very important