I am tongue tied - severely, it turns out, but no one ever mentioned anything or noticed until my own mother, a dental hygenist in her youth, noticed one day when I was about 8 or 9. She talked to my dentist about it: the only reason there might be to clip a tongue tied child is in infancy if it causes latch issues when breast feeding. Other worries with a tongue tied infant are possible speech issues, but those are rare, even in severe cases such as mine. I can only stick the tip of my tongue out of my mouth, but have never had a moment of speech issues or impediments: in fact, I was reading by the time I was 3, so my language skills were always very accelerated!
I am a Stanford trained speech pathologist now (funny I should go into that field!) and I would very strongly suggest against clipping your daughters tongue now, for this reason: clipping it may very well CAUSE speech issues now. She has already learned to talk, her brain has already learned how to "deal" with a "tongue tie", and she will most definitely have to see a speech pathologist in order to re-teach her to speak with a freed up tongue. Because she is 8 years old, there is no good medical reason to clip her tongue now and it will certainly cause speech issues that are not currently present. Is there a reason why you want to have it clipped? I always loved showing other kid's my tongue - they always thought it was cool, and I was never teased about it if thats what your issue is with it.
I will even go so far to say, since we are speaking to each other without children around, it has caused no issues in my adult sexual life either. The fact that it doesn't easily stick OUT has nothing to do with the function of it. I will leave it at that...LOL (that is a question I got from friends once we were in HS.... "How do you french kiss....?" Trust me it isn't an issue.