I wouldn't use the backward loop cast on stitch for an increase either, but recently learned that a M1 away is sometimes called the backward loop. Maybe that's what she meant.
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I still think a different increase would be better. I'd use a M1L or M1R or a knit into front and back. It makes sense to me that using backward loop as an increase method would leave a little hole because it wouldn't be attached to anything at the bottom of the stitch.
And with that type of increase, since you're working into a rib pattern, instead of knitting into the front and back of the stitch you can knit into the stitch and then purl into the same stitch, or vice versa depending on the order of stitches in your rib.