Arnica is great. She can take the pills (they dissolve under her tongue and have a sweet taste) and there is arnica gel that you can massage into the surrounding area (keep it away from the stitches).
Myself, I always keep the stitches moving (gently move them back and forth so that they don't get "stuck). Keep the wound clean. I use H2O2 on the incision and clean off the seepage. That way, the skin bonds to itself more easily (imo).
As the pp mentioned, Vit e oil is good, as is tamanu oil (smells like butter pecan!). But, if your dd has any nut allergies, stay away from the tamanu oil!
Honey is also a very good treatment for skin injuries (especially, Manuka honey)!
Hope she feels better soon!