Hi Donteat...
My DD1 is now Y4, but is often asked to things and we have to say no. Several problems:
we work full time
girls involved in a lot of outside of school clubs/ activities
we want family time ourselves
we regularly go walking on Sundays
we visit relatives & friends at weekends
we frequently travel (usually within UK to see friends now retired & family) during school half-terms
All of this means that often it takes months before we can reciprocate an invitation. We also find that last minute play dates are a nightmare logistically - DH may be away for work - I may have to work late, etc...
So although I understand your DD would like to have friends round a lot - I'm afraid sometimes modern working life doesn't make it so easy for some parents. When I was a child (as I'm sure was the case for you ) we were often around to neighbours to play or go cycling - and it just can't happen like that anymore.
One solution may be to join your DD to various clubs - rainbows, dancing, after school clubs, language clubs, etc... In this way she gets time out of class with friends, but it can be structured (which works well for busy parents).
If you don't work or are home some days of the week - you can suggest that a friend comes home with your DD and stays for tea. You may have to accept that the invitation won't be reciprocated - but I think you have to just overlook that and accept that it may be difficult for the parents concerned to organise the reciprocal arrangement, especially if their are other siblings (one friend has complained that a play date for one, means play dates for the other two - which is 3 afternoons/ evenings eaten up and she just doesn't have the time [she's a school teacher] until summer).
Hope that helps