I'd consider booking her own seat if for nothing else than freeing up your own personal space on the 13+ hour flight. More comfortable than having her on your lap the whole flight.

Also, have you considered checking in 20x20in balikbayan boxes to PH instead of all luggage? It might be more convenient to max out a 50lb box going over, and then just get by with a smaller carryon. Most likely, you'll be bringing gifts / food / items from Costco, etc for family over there, and this is the best way to haul everything.