Hi Mummyloveslucy,
sorry, essay coming up....
so your DD's expressive language is good in that she has wide vocab, able to put together sentences, great understanding but her sounds make it difficult for others to understand her. Thus causing her much frustration. Her errors vary so it's difficult for you/others to predict what she is saying.
In my exp Makaton is typically used to support children with language needs, not difficulties isolated to speech. I wonder how functional it would be for her to use signs if not currently used at nursery.
I think it's great that you are honest with her when not understanding. The temptation can be to pretend you have understood. By showing her you don't lets her know that what she says is important to you.
I would try not to ask her to correct herself (you probably aren't anyway)- rather give her a clear model once you understand her by repeating back 'difficult words.' e.g. she says, 'it's a buttai' you say, 'thats right a butterfly.'
acknowledge her frustration, e.g. 'i can see you are getting cross,' or 'I'm sorry I didn't understand. Let me listen again.' you are doing the right thing by asking her to show etc. Althought it's difficult to see her experience this pain it may help her to gain insight into her difficulty and provide motivation to develop her skills.
sonetimes at this age children do have insights into their own diffs e.g. 'I can't say it...' sometimes they don't and think that others don't understand because they are not good listeners!
Keep up the praise in general.
A really good system that your SLT (when you finally pin her down) might think about introducing is cued articulation- a series of signs for each target speech sound. You DD might really enjoy and 'get' the visual nature of this and will help you/ others at least recognise the initial sound of target words.
When talking to your SLT's manager please mention that DD's errors are inconsistant and it's affecting her behaviour. Tell them just how very anxious you are. Get them to send you a letter of reply to summarise the telephone conversation and to state what they are going to offer. You are intitaled for your DD to be assessed by a different SLT (for 2nd opinion of need) this would be done by a senior. I would ask for this.
sorry for long postx