dd2 wasn't expected to be verbal either (she has oromotor difficulties because her muscle tone is affected due to cerebral palsy). she doesn't have any learning disabilites, her understanding was goo, it was/ is just physical articulation she struggled/s with.
she has had slt from birth (she also had feeding difficulties because of her poor oromotor) so has had a lot of slt. lots of exercises as suggested by bg (although we discovered she has no lateral movement with her tongue - she can poke it in and out and squish it against the roof of her mouth, but can't move it sideways at all - no licking lips going on there
) but also she was introduced to makaton ver y early, so that she didn't get frustrated due to her lack of speech.
makaton allowed her to join in with singing at nursery, (the keyworkers attended courses) and her peer group were also taught to sign and sing along. because it is sign and say, it doesn't hinder any speech, in fact with dd2 it seemed to be really beneficial.
from about 4/5 she was able to use the nuffield verbal dyspraxia programme, which made an enormous difference to her communication and her clarity. she's now completely verbal, and has dropped signing, but still has slt for clarity.
she went straight to mainstream (statemented) with 1-1 (not a unit) but the 1-1 was for her mobility as well as her communication needs.
dd2's speech issues sound very similar - she still has some issues with drooling now (she's 7).
i would disregard the dummy thing tbh - dd2 was never able to suck one at all as her tone was so low.
they tried desperately to get her to use one as a baby as a way of increasing her muscle tone. your dd sounds as though she has low tone, not high.
so in theory a dummy would actually help!