Injecting - Painful shooting up?

[classyfashh]

Swim generally only shoots in her arms just in the inside elbow [the typical place]... She doesn't know if this is bad or what but even after a few days of shooting it hurts to bend her arm or even touch that spot and it feels like there a little peanut-sized bump on her arm where she injected. Of course it's dark coloured, but even if she lightly presses on it, it hurts. Should she be worried or is that normal and okay to continue to shoot in that spot?
Also, when she shoots in the same spot [even when it still is in pain] it is even more painful inserting the needle and pushing the liquid in..

She doesn't know how to shoot anywhere else because she's too scared and doesn't want to hit an artery. She just shoots in the same spot because she KNOWS there's a vein there.