You would homeschool your kid because she got lice, can't come back til it is cleared up and can't get perfect attendance anymore? I'm really hoping that is a knee-jerk reaction to being angry over the situation.
First of all, people need to realize that having lice isn't a sign of being 'dirty' or 'unkempt'. While lice is an absolute nuisance and pain in the butt, please understand that you or your child didn't do anything wrong nor are you lacking hygiene. In elementary schools these sorts of things happen.
Secondly, it should make sense that your daughter (or any other child) does not return to school until she is lice-free. Let's think about this for a minute - say your daughter's classmate has lice and comes back to school before they are clear. Lice are pretty mobile and can move from person to person. Would it be fair to your daughter to have the classmate with lice come back and possible spread it to your daughter and/or other classmates? Now that's something that would make me very upset: allowing the lice problem to spread and continue without taking due diligence and keeping those with lice home until the problem is solved.
As far as the locker - ask for a separate locker or space to store any belongings that are worn. You might get better results if you approach it from the perspective that "I'm concerned that my daughter will either get re-infested or that other children will be afraid that she will pass on lice by having the contents in close quarters". You definitely have a case to argue your point for an individual locker.
As far as the letter about it being unexcused absences - schedule a conference with the principal and let him/her know that if they are denying her the opportunity to attend due to what they conceive to be a 'health issue' (because if they are not letting her come to school because of lice, it is a health issue), then it is clearly unacceptable to deem the absences unexcused. Has your daughter been to see the doctor due to the lice? If so, have the doctor write a medical note and they will not be able to argue that (trust me, I work in a school!).
Having lice can be really upsetting and disruptive, so my heart goes out to you. I wish people would stop thinking that having lice means someone is dirty, uneducated, or doesn't take care of personal hygiene. Those are unfair stereotypes and it is the kid who suffers the most, even though they are typically innocent bystanders who get dragged into the mess. Do anything and everything you can to rid your child and your home of the lice. Good luck to you and hope it passes soon!