Welcome, relblum. I will kick off responses here, although you will probably get a lot of other replies.
First off, how lucky your MIL is to have you as a DIL! What a sweet thing to do for her. I too wear casual clothes, but love to pair H scarves with them. I am sure she will appreciate your thoughtfulness.
To your question about availability of styles in boutiques vs online - Yes, there is wider availability typically in boutiques than what you see on the website. Not all stores get all scarves in all colorways, and of course their inventory will depend on what they have sold that (or previous) seasons. And not all stores have everything that is online.
A few questions you may want to answer - what size will be most useful? 140 cm x 140 cm, as you know, is a shawl size. If your MIL is very petite, that can be a lot of fabric to manage. There is silk (some of these silk 140s feature lighter weight or "summer" silk), 70%cashmere/30%silk, and mousseline (which is kind of akin to the weight of chiffon). Sticking with women's scarves, the next is 90 cm x 90 cm, then 70 x 70 and then (quite small) 45 x45. Once you move beyond the 140s, scarves are typically 100% silk. (Occasionally you will find a wash silk, which has a somewhat softer feel than the traditional scarf).
Of course there are other less traditional formats like giant triangles (half a 140, which some people like because it is less fabric to manage), twillies and maxi-twillies as well.
In addition to size, fabric is a consideration. Some find silk can be a little slippery or stiff. Cashmere/silk is warmer and somewhat cozier than 100% silk. I find silk a little more resilient as it is a little less likely to be pulled or pill than the cashmere/silk mix.
The Plumes is a lovely choice - as you no doubt saw, not high contrast. There are some beautiful neutral colorways of Three Graces, if a giraffe print is of interest (both 90 silk and 140 csgm). Similarly, Jungle Love (leopards) 140 comes in some lovely neutral colorways. These provide a little more contrast and varied looks when tied depending on what part of the scarf you want to feature. There are other neutrals in recent seasons as well that may be available.
Are you near a boutique? If you intend to go in, do call and see if you can get an appointment. My boutique is not really taking walk-ins now.
I am sure others will have many more wonderful suggestions. Good luck!
. Here’s a quick pic from when I brought it home.
