Horse size vs rider size?

So, talking more to the pony club mom who is coming to look at my mare - turns out she's not all that interested because she (horse) is "only" 15.3 hh, which is "much too small" for her 13 year old daughter who is "tall for her age"(is this kid the Jolly Green Giant?). She's really wanting my 16.2 hh gelding (who my husband decided not to sell after all - but I would have thought if anything she'd worry he'd be too big and strong for a 13 year old). I thought it might be a concern about ability to jump, but nope - she just says it is a "tiny" horse for such a tall girl who already had to sell her last "pony" because it was also small. So....am I out to lunch or is she REALLY not picturing the size of a 15.3 hh horse? I've always owned horses in about this height range, and my husband (who is 6'2") has always ridden them without looking or feeling ridiculous. How tall a rider would you comfortably put on a horse this size?