Hi rubles, experienced childminder here again (perhaps I should change my name!)
This is a difficult, but common problem. To take a retainer the place must be available now, you could use it is you wish and it is a good idea to do so, to settle your child in. The childminder is within her rights to charge what she likes to hold a place open until the start date, this is generally half fee, no more.
If she does not have a place available at the moment, but she knows that one is coming up, it would be normal to charge a deposit, set against future fees.
I just taken a £250 deposit for a place in September. I do not have the space at the moment, so could not chaarge a retainer.
BTW, this should all be on the contract you will have signed as there is a special place to sign about retainers and deposits. If you haven't signed a contrcat yet, why has she not given you one?
This is also your guarantee that the place will be available, if not all fees must be returned.
It sounds as though you have paid rather a lot, as beg May is only 6 weeks away, is it for a full time place?