As an owner of two of the common lenses mentioned in the answers here (six-seven months shooting with both) and having shot about 500-600 images with the 18-55mm IS II and about 1500-1600 images with the 40mm STM, I can weigh in that if you are only considering the 40 or 50mm, in my experience the 40mm is excellent and has little barrier-to-entry for a beginner: extremely sharp, feels excellent despite a small focusing ring (weight makes a DSLR similar to a point-and-shoot, barely bigger than a body cap) on a crop body, and with proper steadying, takes very sharp images in low light/flash situations, as well. I would recommend it over the 50mm, as I did not even consider that cheaper lens (40 dollar difference from most sellers right now) given a friend's account of the 50mm 'cracking in half when removed' from his body, and the other generally 'poor build quality' reviews you will find pretty much anywhere online. Yes, you lose 1.5 stops as noted in the comments by moving to the 40mm from 1.8 to 2.8, but as a photographer acclimated to a point and shoot, 2.8 is probably the 'fastest' or faster than she has experienced with her current camera. Additionally, and I cannot speak on this as I have not used the 50mm, most of the more 'technical' sites reviewing the 40mm over the summer generally found comparable, if not in most cases better sharpness in the 40 when put next to the 50.
As is the 'norm' and unfortunately, typical online from what I've seen, the 'kit' 18-55mm is being discounted here, but the 18-55mm IS II (very important, the II w/ image stabilization) is a stellar lens for the price. As a 'used' lens being sold by people who are breaking up their 'kit', I have seen it in the low 100s, from $100-120 but new in the 'white box' from Canon, it costs around $200 brand new, comparable to the 40mm when it was introduced, and twice the cost of the 50mm. So the posts speaking of it being 'cheap' are actually skewed, as this lens new and standalone is the most expensive of the three. You are knocked back to all-plastic construction (versus a more solid 'engineer plastic' 40mm w/ a metal mount), but the price is worth it, as I cannot stress enough, though, how important IS can be for a beginner. In a day with a few hundred shots between my 18-55mm and 40mm framing roughly the same scenes with decent indoor lighting or sunny to overcast outdoor lighting, well stabilized shots (but not tripod mounted) from the 40 tend to have decent overall sharpness with a fair number of keepers, but the 18-55 is consistently sharper with IS turned on, producing the most usable shots for actual prints, including some of the sharpest pictures I have taken with any lens, handheld. What people counting out the 'kit' lens are missing is that this is what you gain with IS - the ability to regain sharpness handheld, even as a beginner, and I don't know any newcomer to shooting with a DSLR that was accustomed to using a tripod with his or her point-and-shoot. More than any other factor, your daughter will probably thank you when she does not come back from shooting and wonder why half her shots with the 40 or 50 are 'smeared' or unusable from low-light or 'forgotten flash' situations. Additionally, the ability to use down to an 18mm focal range should not be understated, as well. There are many more creative possibilities opened up in this range as the wider end of shooting possibilities is introduced. I believe the major 'notches' noted on the barrel of the 18-55mm are 18, 24, 35, and 55 mm (with the intermittent lengths usable, of course), and as a beginner experimenting, each focal length has given me different perspectives on the same scene, as well as helping me from becoming locked-in to a generic 'feel' to my shots. It becomes very easy to see where I was shooting with my 40mm, as a range of photos, even in different scenes, begin to look the same. This is the classic signal vs noise argument (I was probably overshooting this lens early on to get a good baseline of test shots and situations, vs aiming for amazing shots every time...) but still, it doesn't hurt to have the full range, including the 40 and 50mm focal lengths of the other two lenses. Your daughter may not eventually go wider than 18mm once she gets the hang of your 40D, but she may want to experiment well past the 40-55mm range (I found this true for myself, at least), and this is a great lens to have at the shorter end of things if she ever decides to sink some money into mid-telephotos or something with more reach.
So again, if you are only considering the 40mm or 50mm, go 40mm for build quality and overall, it's a great lens. However, if you are a bit open-minded (and I see you mentioned this lens anyway) definitely buy a broken-up kit 18-55mm or purchase it separately - the IS and general sharpness of the lens is great and much more flexible than either prime.