The double sided pedals, flat and SPD would give her both options, and maybe satisfy dad, too. When she is on, say, double track, and it is flat or she feels comfortable, then she can clip in...IF she wants. If not, the flats are always there. The MTB shoes with SPD's are flat on the bottom so would work fine. I was petrified at the beginning on the MTB with clip pedals, but gradually got over it. An 8 yr. old needs to gain confidence first and then learn to clip.

How wonderful that you have this to enjoy together! She sounds like an awesome little girl! Hope it all goes well for you!