When you bring up other girls or check out other girls and the girl you are around tries to act cool around you (By making a joke about it or encouraging you to talk to the girl you are checking out) but she avoids eye contact.

Is this an IOI or a signal?

i'm strongly against overthinking situations like this where you almost have to read the girls mind to figure out what they want. girls are trivial and this will never work out. maybe if you have more than just this to go off you could say it's an ioi? but even if this was an ioi, you'd need at least 2 more anyway to be completely sure. I suggest you do what you want to do. If this girl that you're with is someone you'd rather talk to, then talk to her instead and flirt with her. if you see her as a friend, or she is not your type or some other situation, go for the girl she is saying to go for. you should think about what you want, not about what girl might send you more ioi's or anything.

Oh there were other IOI's but this girl is just a friend to me. I was just wondering when a girl does this if it counts as an IOI or a jealousy spike.

When looking at body language for IOIs you need clusters of signals to be sure. Jelousy is always good to tease a girl with, but if your just flicking your eyes everywhere checking out everything with a heartbeat, her loosing eye contact could be a sign of you loosing respect.

If there are other IOIs along with it though I would say you could count it as another. After you find her doing it, give it a few moments and then give her a chance to get close to you (somthing like a hug, but not in a patronising way) and if she jumps on the chance your good to go. If she hesitates you might have a problem

an IOI is no more than ONE signal, it doesn't mean she into you. Or going to sleep with you.

An IOI is no more than "i like the stuff I have seen till now". Still you can blow this.