If she is currently teething, you may find that's the reason that she's refusing to eat.
Teething seems to be a pretty big upheaval for many babies and as she's not yet 7 months old, eating is a pretty new concept to her.
Have you tried her on different kinds of finger foods and different flavours of purees?
Many babies need at least 3 or 4 intros of a new food before they'll accept it.
My DD will eat most things, but she obviously has pretty strong preferences about things she loves and things she's reluctant to eat.
Have you tried your DD with bread? It's easy to eat and many babies seem to enjoy giving it a good chew and suck.
On the other hand of course, she is only just beginning to learn to eat. It is quite normal for finger foods to be regurgitated at that stage. Eating is more of a game and an exploration, less about nutrition and actual ingestion. She will get the hang of eating and will get better at it with practice.
Right now, even when she gets food into her mouth, she probably doesn't know how to deal with it and swallow it yet, so regurgitation is her only option.
I'm afraid I don't know about volumes of formula, as long as she's wetting and filling nappies, and she's happy and healthy, then you probably have no need to worry.
Different babies drink different amounts and babies also drink different amounts themselves as they go through teething, growth and activity phases.
If you're really worried about her weight, you could either take her to get weighed or even weigh her yourself using your bathroom scales if you want a rough idea.