Over her in the UK we are metric for everything. In shops we purchase our fabric in metres. When we quilt we do it all in inches. None of use appear to have a problem not even the youngsters. If all her equipment is in inches it will be easy to follow a pattern just follow numbers. Converting to make really accurate triangles for a beginner will be very difficult. I would if she insists to buy a ruler with inches and centimetres on. She only has to pull out and look at sizes. I know that centre metres rulers squares are made , but it is going to be very time consuming and may stop the enjoyment.