What to do next?

[ANiceCupofTeaandASitDown]

DD is 4 (last week) and has no speech at all (just a lot of babbling). She has no dx of anything yet but we suspect ASD. Saw Paed before Christmas who said she is still too young . Anyway, long story short, she is about to start in an Observation & Assessment Unit within a MS school recommended by EP, which we hope will help her speech and communication in the long term.
I guess my question is what more can we be doing for her now? I have read other posts referring to ABA - what is it and how do we get that? And mention of the Hanen books - are they any good for child with zero speech? SALT started PECS with her but that had limited success and as she is starting in this unit, SALT has kind of stopped for the moment.
I just seem to be going round in circles in my head as to the best next step.
TIA (sorry for the long post)

Not up with ABA, but my DS used PECs very successfully, which is an ABA style method. If PECs isn't working does using pictures to give choices work at all? It just helped with my DS's frustration to give him a little control, even if it were only for what type of drink he wanted.

I loved the Hanen book More than Words which is suitable for various stages of communication of DC with ASD, including non-verbal.

Others will have info on ABA, hopefully.

I don't know that 4 is too young, some are diagnosed as young as 2! If you want to find out more about ABA then there's a bit on the National Autistic Society (NAS) website, or you could look up one of the organisations which help run ABA programmes (we used PEACH but there are others). It's mainly for early intervention, the younger the better, although it has been effective with older children too.