I'm sorry and I hope this does not come across as crass, but I have a real problem with the comment that you "are the boss." Your baby is just a baby and not trying to manipulate you by the fact that she wants to choose when she eats and how much, or by holding her own spoon. And I'm pretty sure she was truly upset that she thought you were taking food away from her and not crying fake or "crocodile" tears.
The good news is- if she is reaching out for food, then that is her cue to you that she is definitely ready for solids. A 5 month old still needs formula or breastmilk, so I would not cut that out, but I would continue to do what you are doing with the solids.
My suggestion is- like the others said, let her help feed herself and deal with the mess. You can hold a spoon and help her while she holds her own, that way if she can't "shovel it in fast enough" you can help with that and pick up her slack.
She's probably just now getting interested in the solids, actually. It's generally not recommended to start solids until 6 months of age.
Is she sleeping 12-14 hours straight?? This would concern me. Her tummy is probably VERY empty when she wakes up. I would speak to your pediatrician if this is the case. He or she might suggest that you wake her up for a feeding.
Also, you don't say that you are even giving her lunch??
A great product to try with a piece of apple, banana, etc. in it is the baby safe feeder, which you can find here: http://www.onestepahead.com/product/osa/307755.html
It can help her feel like she is in control of some of the feeding, is easy to hold, and will keep her from choking when she sucks or gnaws on "real food" in it.
Good luck. I really don't mean to be judgemental, but please pay attention to your baby's cues. She will tell you when she is hungry and what she wants. It's not about OUR convenience when they are this young! Parenting is hard, but sometimes we make it harder when we try to put them on routines rather than just "going with the flow."
Good Luck!
Amanda