I 30M feel like my 27F partner has been unwittingly singling out my child when it comes to parenting vs her children.

So my partner and I have been in a relationship going on 2 years. She has 2 boys ages 6 and 7. My daughter is 5. We waited the right amount of time before introducing each other to the others kids.
We have since moved in together and built a nice home. Mind you we aren't married, just trying to have a great family life before deciding when to get married. Our kids get along great, practically inseparable. My issue stems from if I ever try to offer disciplinary actions or parenting advice she does not agree with, most of the time I am met with a cold "would you do that with your daughter?"
Or if she's upset she always refers to her as "my daughter" I never refer to the boys as "her sons" I do not want the kids so feel separate they already see each other as siblings. It could be something as simple as ripping off a bandaid or giving a stricter parenting advice.

I have been a step parent before so I know my boundaries with someone else's child such as being to severe with punishments or hitting are big no no's.

She has not.

I've never dealt with this kind of behavior and not sure if it's a bad sign or just he lack of experience when it comes to dealing with a significant others child. She is very caring with my daughter and feeds her well and is patient, also does her hair everyday for school and helps with the feminine advice I as a man wouldn't know about.

We just had a big fight about this subject and she said she means no offense and if I'm offended then that's my issue.

But I can't help but be offended at my daughter being brought up as a comparison whenever her parenting is given advice or even somewhat critiqued.

Not sure if I'm overthinking this.