They can be in pain without being lame, not to mention the fact that many people will miss bilateral lameness.
A horse may test a rider, but it wouldn't continue to do so nearly every ride. I've been around horses many years, seen a lot and ridden a lot and that just doesn't happen. They may, if that way inclined, take advantage if you aren't paying attention but that would be your fault not theirs. Some may be sharp and reactive by nature, but that's a different issue to yours. You may or may not have been a bit young when you got her but you could do more with her then than now so something has clearly changed.
With the behaviour you describe the only advice I'm prepared to give is get her checked over by a vet who you've explained the problem to and then, if she gets the all clear, get some lessons on her. The behaviour you describe is too much to give advice on on a forum. What I would do with her, beyond a vet check is hard to say since it would depend on what I saw and felt, but as a rule I feel that a horse that rears properly as opposed to just coming up slightly is either desperate or means business and I would seriously wonder if it had a future as a ridden horse. I've seen some very bad accidents from rearing when horses have gone over - it makes no difference to the rider whether it was accidental or deliberate.