Luke thought about how she'd organized the evacuation from Hoth, not even thinking about how she was going to herself off the planet. She had searched for Han when Jabba took him and then put together the rescue plan and while it had some rough spots, they had gotten him out of there. "She is. I learned not to underestimate her not long after I met her. She's also been through a lot that I don't even know about I'm sure."
Being the youngest member of the Imperial Senate and also guiding the Rebellion couldn't have been easy but she'd done it. Watching her planet be destroyed would have broken a lot of people but she had gathered herself and gone on. He was sure that she'd let herself grief at some point but she wasn't the type to let just anyone see it.