cancer

hi my cat tiger was 10 years old she has always been distant not bothering to fuss much.,now around 3 weeks ago she started fussing me up licking and playing, my daughter was amazed how she changed,anyway this playing went on for a week, then she didn't come down stairs when she did she ran and hid,avoiding me as if i was going to hurt her
i noticed her limping quite bad on front left leg, i thought it might be sprained over the next few days she was holding her leg up completely, so i took her to the vet in case it was dislocated he phoned and said it was a massive cancer and she would have to have leg and shoulder amputated, what a shock anyway my mom decided best thing was to have her put down, i was heart broke as i said i don't think a cancer could start so quick i wondered if the vet had got it wrong and it was dislocated and tiger was put down unnecessary,i cant sleep worrying about this sad incident  also when i collected tiger from vets blood was coming out of her nose i wondered what could have gone wrong to make her nose bleed await your reply thank you