I'm a bit confused about why Rossweisse would be so sad about Leon being in a coma. Didn't they have a totally antagonistic relationship prior to them having children? I'm guessing that having children mellowed her out, or maybe she already had feelings for him prior to his capture.
She was unhappy about the situation and Leon's coma was a part of that. The author wrote, from Leon's perspective, that dragons are very prideful and their personalities cause them to seek revenge and dominance when they feel wronged. Dragons also measure each other's value through strength.
Leon's use of the blood ritual caused her to have his children. Firstly, that makes her a dragon king with half blood children of a dragon slayer. That's a big taboo. She cannot openly discuss their parentage. Doing so would put her position as king in jeopardy and invite talk of her weakness and incompetence which decimates her pride as a leader. It would also invite ridicule of, and potentially a limited future for, her half-human children. So, the existence of that secret decimates her confidence in being a capable and protective mother. It's clear she cares about them so this has to also be emotionally painful.
Secondly, the author said dragons mate with only one partner in their lifetime. So, Leon shut off whatever plans or hopes she had for her future as a spouse or parent.
Rossweisse kept Leon alive to exact revenge on him for this. She wanted to salvage her pride. But, he was in a coma. So, what could she do? Abusing his unconscious body wouldn't accomplish revenge because he wouldn't know anything or react. It would be the same as if he had died. She was stuck.
All she could do was wait for the bastard to wake up. That might have been days, years, or never. She couldn't share her frustration or worries with anyone. If she tried then she'd have to explain why she wanted revenge which would reveal these secrets. The whole situation was depressing.
She probably was sad, and maybe mad, sitting by the bed when Noah saw her. It didn't mean that she had romatic feelings for Leon at the time.