Well I hope you do get 13.
Frogsleap posted a very interesting blog some time ago, about the skewed ratio of small vs large fruit in crosses of small X large. His findings, you actually needed about ten plants to find one large fruited, because the ratio is skewed towards small.
I have to say, my own results have pretty much agreed with that observation.
So you may only get five out of 55 that are close to the size of the large parent.
OTOH you should get lots of intermediate sizes as well, and maybe a lesser amount of "bigger" than HM is an easier target that would satisfy your mum as well.
