Yes. Crusher really behaves in a way that is below her. She is a respected Chief Medical Officer on the Federation flagship. Clearly she is intelligent and capable in her career.
Yet she makes the same mistake many of the women on TOS do - she gives it all up for "love". She's willing to suddenly rearrange her life and leave everything she has worked for just to be with an energy being who has shown no remorse at harming her colleagues. Especially considering that she's not prone to flings, this really seems out of character for her.
As somebody else said, I think the fact that it's so out of character is part of the point of the episode.
Sub Rosa is actually one of my favourite episodes of late TNG. I think there's a lot of interesting stuff going on in the episode. The way it uses tropes from romance novels isn't just to do a bodice-ripper in space episode. I think it can actually be read as a damning critique of the roles sculpted for female characters in those books.
The way I see it, the scene where Ronin "merges" with Beverly for the first time is quite ghastly. She screams 'no' and 'stop' repeatedly. From then on the entire relationship is coercive as he uses her for her energy and manipulates her emotional state. Because it's dressed up with all the fun paraphrenalia of a gothic romance, it feels like a love story, but it really isn't. It's abusive as Beverly is isolated from her friends and career and made completely dependent on Ronin. (I read a good 'fic once which dealt with what Beverly went through in terms of a drug addiction with Ronin as a pusher, which is another interesting analogy.)
It's also interesting coming in the wake of
Attached, where Beverly completely failed to conform to the narrative and live up to her original sketchy character brief as just "Picard's love interest".
The episode's not perfect. I could have done without the headache of trying to work out the Howard name. Also "I did fall asleep reading a particularly erotic chapter of my grandmother's journal" may be the worst line ever spoken by an actress on prime-time TV. And I think the final scene where Beverly wistfully says that he made her granny happy falls a bit flat.
Still, in a series that was trying (if not always succeeding) to do better than TOS in not having women completely subservient to love, I think it's a clever story. It's not a comfortable episode, but it's not meant to be. I reckon the fact that so much of fandom comes away from it completely creeped could be seen as a point in its favour from that POV.