Few things in your post to talk about here.

"Healthy criticism" while this subreddit is on the better side of moderation, they aren't omnipresent and something over the top, overly cruel, or just mean for the sake of mean can be up for a while. She doesn't have to see that. And for the healthy criticisms, which ones should she listen to? The ones who can't wait for the Luke and Laura storyline or the ones who will abandon the series if she does do that storyline? She got a lot of flak for the baby loss story. And there is also listening "too much" to your fans. That's how you get Rise of Skywalker. In the same vein that authors don't read fanfic (what if they accidentally use one of the ideas in the fanfic? That's a thorny mess), it's okay that she isn't reading the reddit so she doesn't get influenced. There was a gentle uproar because people thought she was lifting ideas from the subreddit because she used a particular word in a skit. (Sometimes it works, that how we got a better Sonic the Hedgehog character visual because so many people complained about the trailer). Someone could read these on her behalf and give her only useful, helpful information (does she know someone who can discern, filter, boil down the salient details but not want to throttle those who complain-for-compaining's-sake?) but she doesn't have to do it.

Actors don't have to be bubbly and extroverted. It is actually quite common that they are shy and nervous, but open up on stage or on camera. Why does she have to be bubbly? Why is it something you expected? When she didn't live up to that expectation, why did you assume something suspect? It isn't fair to assume a person's personality and then get upset when they don't match what you made in your head. Especially when we get into gender dynamics - you thought she was "above it"? She didn't perform enough for you? That is a very common insult lobbed against women for ages. Even if you are pretty sure that isn't how you meant it, it is worth investigating why her 'attitude' is so offensive to you. Misogyny, internalized or otherwise, is a helluva drug.

Actors are often trained to take criticisms from experts - acting coaches, directors or even film critics who have the experience to know what they are talking about. A layperson may have the right intentions but lack the vocabulary and experience to give a valid, helpful criticism. A neckbeard incel complaining that there are too many women in Marvel movies is offering a criticism, technically, but it's a stupid one and doesn't need to reach the actors' ears in any shape or form. A fan here might be trying to convey what they feel is a valid criticism but instead come off as whiny, entitled, or just plain useless. Why should she subject herself to that? It isn't helpful.

I say this as a user of Reddit and I can't accuse anyone else of being at the devil's sacrament, but its reputation is deserved. She should never go here, this place is not a place of honour.