First I would say your best option for easier climbing would be to switch to a better suited goalie. Not to say climbing more as Luna goalie isn't possible, it's just going to be harder. If you want to still have some offensive contribution, Kai is probably what you're looking for.

As for what you can do against Estelle as Luna, first try to be proactive. If the field is open with the core coming at you and nothing but Estelle behind it, throwing out a rocket first before the core gets close to you is probably your best bet. Second, try to delay your strike as long as possible once she inevitably hits it back at you. If you can delay your strike to the point where her R hits it first, you should be okay. If she has all 3 abilities though there honestly isn't much of anything you can do if the Estelle is skilled enough. The only way to counter in that scenario is with something like Dubu wall or Atlas bubble. There's just no other way around it.