check to see what size her tires are? thats what you need to know, doesn't really matter what wheel. if the width is 18, 19 or 20 she would need the smaller 18-23 ones. if they are like a 22, 23 or bigger she'll be fine. i would check the rim and rim tape as well.

luke

The size on the outside of a tube box is typically rather arbitrary, as are tire measurements for that matter. One companys 18-23 might be anothers 20-25 and vice versa. For the most part tubes are sized a good amount smaller than the space they are intended to fill, how much smaller is highly variable. This means that a variety of sized tubes will fit the same tire. The shop sold you a tube that should have worked fine, dispite its slightly larger size. An increase in size will make it more likely that a small amount of tube will sit between the bead of the tire and the rim, the likely cause of your blowout, but this is more a problem of a less than thorough installation process, not an incorrectly sized tube

if the tube blew while you were pumping it up you most likely had a bit of tube pinched under the tire... or you had something foreign and sharp in there either in teh tire or due to too narrow or worn rim tape... if you still have the tube check to see shich side it blew on, if it is the side it is the tube getting caught, the inner would be the rim tape and the outer would be something in the tire...

in answering your specific question, the wider tube should be OK unless she is running a very skinny tire, I almost never see tires narrower than 20 so not the shops fault...