I spent the last 5 months traveling Europe and found that young female solo travellers made up a huge percentage!
Guys tended to travel in 2s or 3s, and girls tended to go solo because they often couldn't find other girls from back home to go with them.
But girls tend to find other girls to pair up with...and cling to groups, and make friends easily. If you are looking like a tourist or not on your guard in a big city, anyone can fall victim to crime, no matter age or sex.
I am not sure where you and your daughter are from, but I would say that it is more dangerous to traveling around the US or UK than it is to travel through most of Europe. To be honest, I felt more "on-alert" in places like Glasgow, Liverpool, or Pittsburg, than anywhere in Europe...even Bosnia!
Places like Germany, Switzerland, Austria, Belgium, Holland, Denmark, Norway, and Sweden are incredibly safe. Places like Poland, Czech, Slovenia, Croatia, Hungary, Slovakia, etc are usually quite safe. Places like Spain, France, Italy are less safe generally...gangs, tourist crime...but it can also depend on the city or region...like how Naples is known to be more crime-riden than a place like Florence, or Marseilles for violent than Lyon.
Find a backpack which has hard to access zippers so that no pickpocket-ers can snag anything from your bag if your back is to them.
I never wore one of those money pouches either...just try to look normal and not like a tourist when you go out.
She will know to keep her hands on her money in her front pocket when she needs to.
Tell her not to wear any fancy jewelry just in case it gets lost of stollen. Generally hostel are all fun-loving and safe, but there are times where poor travellers and shady people get their stuff nipped.
The most common story I heard was people having their mobile or iphone nipped out of their purse while partying at a bar...or getting a backpack stollen while leaving it on the beach and swimming in the ocean.
If she is bringing a DSLR or laptop, you can probably insure it under your home-owners property insurance as a one-off item, or find travel property insurance. I did this for my valuables.
She should also bring a small pad lock or combination lock for hostel lockers.
She will be fine! Hope that helps