my mum's been knitting this pattern http://www.dailyknitter.com/sophia.html on size 7 straight needles, but has been having trouble getting row 21 to leave the holes of the lace effect. Can anyone offer some insight?
I think the needles may be too small - pattern calls for US 10.5.
The holes may be more visible after blocking if she's using a natural fiber, but since pattern materials list an acrylic yarn, it looks like it doesn't have to be blocked (nothing in finishing section about blocking either).
"The cat has too much spirit to have no heart." -- Ernest Menaul
Your're right the YO, K2tog on row 21 will not really make much of a size difference in the hole from what has been done in all the other rows. Maybe she would like the effect of doing a double yarn over and then working into the spot where the double yarn over is in the next row only once and letting the other loop fall off the needle. It will make a bigger hole that way. She could try it on a sample and see if it is more what she has in mind.
Sometimes you have to take matters into your own hands. :-)