I do volunteer work with a local ARC and I've never seen anyone of the fifty or so learning disabled folks associated with the organization with a speech problem resembling Shannon's. (I'm going to discount the idea that she might have cerebral palsy) In fact, the opposite is a bit more common, in that the person with special needs has no problem speaking at normal speed, but sometimes when they get excited they can go even faster and become incomprehensible.
There's one universal trait in them and I wonder if Lynn's going to show this in Shannon or has even noticed it, and that's that they have difficulty picking up on social cues. Sometimes it's more stark and they can't always socialize in a way that others find acceptable. In the former example, it manifests itself as, for example, laughing inappropriately, fixating on one thing for hours, yelling at the wrong times, talking about inappropriate things in mixed company, behaving like an eight year old when they're teens or older, that sort of thing. For the latter it can get more serious like genuine anger/rage over minor issues like getting the wrong drink, masturbating in public, or even sexual assault. I almost invited an attractive girl friend of mine out on one of our recreational outings, until I realized that one of the guys probably would have assaulted her. (Nothing truly serious, but to a woman who doesn't know him, incredibly awkward and embarrassing) There's a lot that fully abled people take for granted when it comes to conducting oneself in public. When you spend time around folks with serious mental deficiencies, you recognize that.
And it doesn't make them bad people.
I wonder if Lynn's going to show anything like that, even in its mildest form, or if she's going to continue to sugarcoat Shannon and paint her as a little angel with no faults or foibles or (if you want to make it less negative) idiosyncracies except those that other people ascribe to her. Hell, I'll say that it makes April a much bigger person if she can see Shannon as a living, feeling human being in spite of the fact that she does some weird, socially embarrassing things from time to time. It'd also give some depth to Becky's rejection of her, but if done right, it shouldn't validate her feelings. She'd still come across as shallow, but at least we'd see what exactly it is she's objecting to Shannon over.