I boarded from the age of 8. I don't have abandonment or attachment issues and I'm very close to my parents, I certainly didn't feel like an inconvenience to them. I think people are really projecting their own feelings here. Boarding doesn't breed issues just by virtue of it being boarding. Sure, it doesn't suit everyone, but at my junior school 90% of kids boarded (including many who lived close enough to the school to be day pupils but requested to board as they felt they were missing out).
I think it depends on the school, but no, it's generally not like Mallory Towers. That being said, I went to a lovely, rural junior school with ponies, pets, open fields, loads of outdoorsy activities. Perfect for me as an outdoorsy, horse riding, animal loving child, and I loved it. By contrast, I went to a senior school (which I chose) in a big city, very urban, very different focus, and I absolutely hated it. Nothing to do with the boarding, just a different ethos, different pupils, different style and it didn't suit me. Let your DD go for trial days at different schools and really do your research on them and make sure their values and ethos tie in with your own. No point sending your DD to a sporty school if she isn't sporty, or an artsy school if she isn't arty. They'll all have specialisms, and she's more likely to find it difficult if she doesn't fit in with them or they're very different to her upbringing.
I would send my DS to boarding school in the future if we could afford it, but I'd be very careful that the school tied in with his upbringing at home and that their focus tied with his interests and the activities he excelled at.