I think your daughters plan is an excellent one. Mechanical Engineering is a more general degree than Aerospace Engineering, with significant overlap in many of the courses. In fact, in the US, many departments are combined Mechanical and Aerospace. As far as job prospects, both degrees open many doors and one degree will not likely be better than the other. In the US, companies like the fact that engineers know how to work hard, focus, and develop evidenced-based solutions for problems. At MIT, many Aerospace Engineers actually get hired by financial companies because of their mathematical abilities! So you should not worry too much about her desire to choose Mechanical Aerospace, both will provide her an excellent foundation.
Mary (Missy) Cummings