OP if your DD is obsessed with minor imperfections on her face then it's very possible she has Body Dysmorphic Disorder. Researching cosmetic surgery obsessively, obsessive mirror checking of the "flaws" and seeking cosmetic surgery are all symptoms.
A good cosmetic surgeons should be well aware of BDD and be screening for it but of course people can lie and so pass any screening test.
I am not saying this to worry you but BDD is a serious mental health condition with a high suicide rate. And cosmetic surgery will worsen the condition. So plastic surgery is NOT recommended for people with BDD. And an attempt to seek plastic surgery needs to be taken very seriously. I've said this because there are a lot of answers on this thread telling you she's an adult and to leave her to it. Assuming she has BDD, this is not a simple case of a parent not liking an adult child's decisions. If she has BDD she.is not thinking straight. And knowing what that is like I would argue that her decision making capacity in this area is impaired (as evidenced by the fact that she would not be allowed to decide to have plastic surgery if a (reputable) surgeon knew she had BDD)
Have a look at the BDD Foundation website and perhaps give them a call for advice. I have BDD and if this were my child with BDD (assuming she has it, there is a screening tool on the BDD Foundation website) I'd be calling the plastic surgeon and telling them. Generally plastic surgeons do not like operating on people with BDD because there's a very high likelihood they will not be happy with the result and will complain. So even if they don't care about the mental health of the patient, they will likely care about themselves and their reputation and them and their staff having to deal with a hysterical patient.
Tbh a good surgeon should be able to weed out a BDD patient on the basis that the imperfection(s) is tiny or unnoticeable to others but I think plastic surgery and seeking "perfection" is becoming more normalised so it may be harder for them to notice.
As someone with BDD one thing that puts me off plastic surgery is the thought of what happens if it goes wrong. I could end up looking a lot worse So another tactic might be to discuss that with her and ask her if she's researched what can go wrong with that particular surgery and what she would look like if that happened. Not all plastic surgery failures are fixable.
The BDD foundation have loads of information about the condition on their website. They have a helpline to get more info and they run an excellent group "therapy" session. The challenge usually though is getting someone with BDD to realise that they have a mental health condition, to accept it and then that they need to seek help for it.
Best of luck. This must be really frightening for you.