Sounds like I need to grab the book (tonight)... My recently refreshed memories of the Shadout are exactly as you say this film has her, not being a big enough part except...
as an in-universe Miss Exposition to clue the mother in on local lore/prophecy, and then after the year of unexceptional but loyal service gasping her last in barely half a clue as to Whodunnit
...that, when I first read the book, I wondered why it couldn't have been the Coded Pot-Plant to do the first half. Yes, there's The Object to pass on (there were other ways to do that, and especially as it's barely even a McGuffin in the first half of the book), but the presumed reporting back to the Fremen of how special the new landlords may be could have been done via that dinner-party (with another yet-to-be-revealed major figure who still ends up being Game Of Thronesed out of the plot later, after fulfilling further thread-linking purposes).
The gender thing... It's an androcentric plot, as written. Much of its time.. The mother's sisterhood is respected/feared, but individuals at her level are at the whim of their consorts' opinions (within the scope their trained influences upon them allows, but she herself seems to have been content to use the lightest of light touches upon someone who is conveyed as a decent man, probably even without such possible feminine wiles). The most galactically recognised public female figure of importance (Lady Not-Appearing-Until-The-Next-Film?) is to be cruelly sidelined
by the hero!. The Reverend Mother, the Shadout, the future heroine-consort and the Child(-Also-Not-Appearing-In-This-Film...) are all special authorities or (come to be) respected within the narrow scopes of their own communes/communities (with or without misogynistic overtones, which special-status balances).
Actually, it's not far from the current standards, except where specially countered (I can't quite work out how they'd do Ann Leckie's
Ancillary trilogy, in film, without spoiling the beautifully preserved ambiguity of that work's characterisations). A single gender-flip from the source material is trivial, on occasions it is attempted.
(c.f.
The Watch mini-series, which gender-/age-/race-/profession-/ability-/attitude-flipped a number of 'named characters' in pointed ways that annoyed even progressively-minded Pratchett fans - because it made for a complety different far-end-of-the-probability-curve universe from the books and established mythos... Even if it's a Multiverse (and Trousers Of Time) thing, as implied, this is a sub-multiverse different from the book-type sub-multiverse (mostly shared with the prior TV animations/mini-serieses) suggesting that there's a meta-multiverse level one further level out if you wish to creat a Grand Unified Theory of the whole discverse..)
...I'm typing too much. So, Lasguns to finish (for now). A shortened point I was going to make was that I took the book-reason for their uselessness (or, rather, they became a MAD-solution) was of a Rock/Paper/Scissors nature, coming up with a reason why they should not be as useful as they should be in any other similarly-teched creation. Similarly, artilliary is supposed to he useless, but because (spoiler) it's actually useful... After a fashion. Writer's choice to have done it that way. The faithfulness of it being re-written in this movie I accept the views of those who have seen it, for now. (But there are other ways to RPS lasers out of primacy, with personal shields if necessary, that might have been used.)
End post. Maybe more later...