Sashing for 25" blocks
 

I'm making the Big Star Quilt from the Missouri Star tutorial - never could find a printed pattern for it. So that I don't end up piecing the sashing (44" WOF - 25" sash will leave 19" piece), will it work if I turn the fabric and cut 25" pieces horizontal to the selvedges?

Yes, it will work, as a matter of fact strips cut parallel to the selvedge have less stretch, so they keep the blocks sized better.

If you use her method of making HST, I think putting the sashing on the lengthwise would be good to help stabilize all those. OAS edges.