Bad parent alert = I thought DD's lisp was sort of cute. Now she's 9, I'm worried

[LarfingGal]

DD is 9 and in her penultimate year of Primary school. She's always has a lisp. She says the th- sound instead of s- (so thos-ages, not sausages, or preth-ent instead of present). I've tried to get her to make the s- sound, but she can't seem to put her tongue behind her teeth and just can't seem to form the sound with her tongue so it comes out.

I am totally aware that she won't get any SALT under the NHS for this - it is her only speech issue. So, what can we do at home to try and get the s- sound coming, and stop the th- ? I admit it was cute when she was little, but it makes her sound like a baby now and she's going to be annoyed by it soon.
Please don't say I've left it too late (I really fear I have...)

You could try telling her to put her tongue in the place she would for a 't' and then adding a 's' by saying 'ts' like the sound at the end of the word 'cats'. And keep reminding her to not move her tongue forward. You can also use a mirror to show her how different sounds are made.

Thanks for responding ThatsWot. I've just got her to try that and she can't get it. I think my tongue has a different shape for t than for s, so I imagine hers does too (with t- my tongue is on the roof of my mouth and with s- it is sort of curled up a bit in the middle of my mouth?). DD says ca-th for cats anyway, so she doesn't have the ts- sound at all .

How to stop her moving her tongue when it is obviously the most comfy thing for her?

Hi. My son went to speech therapy for a lisp when he was 4. He went for about 6 to 8 weeks and I was amazed by how quick the change was. She played games with him and we had to practice him doing a ssss sound. I couldn't get him to do it before we went but she had some really good ways of getting him to oractice.
Why do you think you wouldn't get speech therapy on the nhs? You can self refer and I think this would be entirely appropriate.