One can only assume that team building means one of 2 things "How do I get my girls to like or get to know one another better" or "How do I get them to play better as a team"? I'll try to address both below...
If we are talking getting the girls to like each other or getting them to know one another better your options are plentiful. To begin, I am a huge fan of team dinners I don't think anything creates relationships as well as breaking bread. If you have the parental support on your team it would be awesome to have a parent who would be willing to host the team dinners from time to time letting the girls to get to know one another outside of softball.
Other ideas to help the girls get to know one another include: scavenger hunts, snap chat or video/picture challenges, laser tag, goofy games at the end of practice like front of the boat back of the boat or dizzy bat races. I have actually gone so far as to Saran Wrap the team into 2 teams who have to work together to maneuver themselves around the bases. First team to finish wins. Just be warned if they don't work together they will fall so there is a small potential for injury, which is something you want to avoid if possible during team building activities.
If we are talking getting them to play better as a team, the options aren’t as cut and dry. The best way to create a team is to talk, teach, and preach team to them from the time the girls show up for tryouts. Making sure that they understand the only rule you have is to do nothing that hurts the team. That rule pretty much covers all the "bad" stuff that could cause problems on a team. Show up late, nope that hurts the team. Get bad grades, nope I'd be ineligible and that would hurt the team. Have a bad attitude, nope that would hurt my team. Didn’t call a fly ball and it drops between me and two other fielders, that hurts the team.
As a coach, be invested in your players, really care about them. Take time to find out what is going on in their life and take that into consideration when their play waivers. If you know a child is having home problems and she is not playing at the like herself be sure to check in with her and not punish her for poor performance as long as her effort is good. Life problems do not excuse behaviors that do not put the team first. Developing trust goes a long way when building a team.
Typically when players "misbehave" it is to get attention so the best advice I can give you when you have a player who is exhibiting less than desirable behavior is remove them swiftly and continue giving your attention to the girls who are NOT hurting the team. When time allows go over and address the behavior of the other player letting them know specifically what was unacceptable and what an acceptable alternative action would be.
Encourage and cultivate a competitive environment. Reward the winners instead of punishing the "losers". If you are doing timed races of like players (players of similar athletic ability) why punish the loser of the race for being slower than the other girl? Speed is not something a player can control and running her more will NOT make her any faster it will only make her hate conditioning. Reward effort, if she runs that one race all out, full speed, nothing left on the table after, then reward her for the effort and let the winning teammate move on to the next round. She will get tired of being first out of the races and work that much harder for the team next time.
I could continue on and on about the different things that go into building team, but without knowing the exact issue you are looking to correct this is the most encompassing answer I can provide at this time.