"You're used to how your DD speaks, and I know as a parent of a DS with a speech disorder that it's very easy to just get used to little oddities, and not hear what others hear."
I'm not picking on you Hassled, I know that's a common perception, but that sort of generalisation drives me InSane(!!!)
It was always us saying that DD and DS2's speech wasn't good enough, asking preschool about it repeatedly. Preschool repeatedly implied that we were unnecessarily worried, and I have even come to think I may suffer from APD myself. Meanwhile, we in the family were the ones who struggled daily to understand youngest DC. Only to encounter an assumption from other parents and some professionals that DC probably only developed such bad speech because we in the family somehow 'enabled' their bad habits -- when I was always saying things back to them correctly when I could work out what they meant. We were the ones struggling like crazy to understand what they said, and sometimes we were the ONLY ones in DC's lives questioning whether there was a problem!
The most common annoying comments were:
"Oh, the problem is that the older ones talk for him" (er, no, they're as baffled as us what he's saying, and they keep asking now that he's 3yo when will he start to talk)
OR
"Oh, you're probably used to the way she talks" (nope, I have to make her answer yes/no to questions to have a clue what she's on about -- and she doesn't even say yes or no very distinctly).
The first sodding set of questions from HVs were all about whether my DC had a systematic speech disorder that somehow we in the family had adapted to -- drove me crazy that. If it was systematic and we could easily suss out the system, I wouldn't be repeatedly asking for help, would I?
Okay, off my soapbox.
OP: maybe just ask your a load of casual friends if they can clearly understand your DD. That will be the outside check that you need to verify what you think you know already.