If she was really Failure to thrive wouldn't she NOT meet milestones? But she seems to meet them before the "average" so that would tell me she is perfect. But 3 months clothes at 7 months? That's really scary to me.
Yes, this is the main reason docs worry about small bubs - that they are FTT - but FTT is really characterised by dropping down the centiles on the charts and failure to meet milestones. DS was also meeting milestones early.
I can't find a site where you can put her weight in to compare it, sorry.
On the fenugreek, oats, etc.: If you are dealing with an oversupply issue, these things to make more milk will only make the problem worse. Eating high calorie foods like avocado, coconut oil, etc. would be better, as it should increase the calorie content of your milk. Increasing your supply further is a bit like you drinking more water to gain weight whereas adding caloric value to your milk is more like you drinking cream to gain weight - which would work better?
From what you're saying, it sounds like she's doing fine.