Panchita

I was born and raised in Scotland, but also lived in Texas for a while, and would say that the religious element is probably quite a strong part (there is a reason why Texas is part of 'the Bible Belt') so you may need clarification as to denomination as well as strength of desire for this to be included (since to me religion wouldn't really be an obvious factor in a 'traditional Scottish' quilt, but your - or your client's - views may vary from mine).

I would also expect a desire for significant use of tartan ("plaid") in fabric prints and/or piecing (I'm thinking of sashing, tho that could be rather complicated).

My first thought re design (taking into account the above) was a centralised cross with a thistle twining up it, then borders incorporating tartan and saltires.

You might also want to consider wildlife (e.g. stags), plants (thistles, pine trees etc.) and scenery (e.g. mountains) for fabric prints, piecing or incorporation into the quilting itself, since that is usually a strong association re Scotland.

Another thought: it is anticipated that the quilt top will be pieced, appliqued, or a mixture?

Edited to add: also (tho personally they make me twitch) don't forget about bagpipes if going with the musical element.

Edited again: is there any way you could get pre-approval of your design from the gift-giver? It's all very well us going with stereotypes and general impressions, but for a bespoke gift that will be best for this particular lady some input from those who actually know her would help no end!

I'm shutting up now :-)