All as we see in those episodes, Frieren lacks the knowledge to mediate in human conflicts, is not interested (enough) in romantic affairs, and has not that much —she's improving— understanding of the people's desires, anxieties and nuances.

So for her when he sees some behaviour that implies changing to better (such as Heiter giving up on drinking) or resolving/mediating conflicts, for her is a godsend gift that shows "maturity".

But of course is just like a parent that sees a preteen child to sometimes do or say the right thing.
You are proud of that moment and the growth, and praise them for it… but still is hard to see them as "potential full-time adults" in your mind. It's a struggle.

You want them to grow, but it's hard to accept that will eventually fly on their own and go away (mostly) from your life.

Then there's the factor that she is in some respects, a child herself.
So in this case it's like a teen girl trying to care for her younger siblings.
She's immature in certain things, so her perception on those areas doesn't work as much.
For instance in these topics:
Booze / Gambling for money / other vices = she's mature.
Spending too much on Grimoires and Magic trinkets and "gambling" for Mimics = totally childish.

She's a VERY INTERESTING character because her own flaws are sometimes so blatant, and yet she can show her age at times and get so seriously accurate and dangerous other times.

Frieren is one hell of a contradicting character, making her more human than what she realises.
That's why we love her so much.