Most of MH patterns specify a "scant" seam allowance.
Practice a couple of blocks first and compare to see which technique was more accurate/or easier for you.
If you have a 3.5" and 4.5" ruler, this will help you tremendously to achieve the blocks MH designs because most 12.5" blocks are broken down into 3.5" or 4.5" units unless you're working with smaller pieces then it's 2.5" units.
I like her patterns and I had the same problem before until I came up with my own short-cut technique.