I'm about to purchase a road bike for my daughter. I'm looking to purchase the best bike for the money in the low end, as she'll grow out of the bike over the next 4-5 years. As I look at the bikes, I'm torn with Sora, Tiagra, and 105 differences. I'm hoping to ride with her as much as possible and would like to give her every reasonable benefit to keep up with me so I don't have to slow down as much. I'd also like to make sure I purchase at a level that will reduce maintenance and difficulties.

So two main questions.

How much difference is there between Sora, Tiagra, and 105? I was hoping to go 105, but the cost may be too high. Is there a line I shouldn't go below?

Also, I have Ultegra & 105 parts that I may hand down over time that I'd like to swap hers out for the better parts, such as wheels with an ultegra cassette with a better set of wheels. Are they compatible? Or does the derailer match the cassette? How about shifters? etc..?

Thanks