I would continue to talk to the school. If you feel your child is harrassed or bullied by this boy - the school needs to take action. If they are reluctant - stay on them.
I would have your daughter meet with the school counselor. It is a resource that I think many forget about (I did). Use it. It is available to you and your daughter. You should just be able to contact the school and ask that your child meet with the counselor. You should also be able to speak to the counselor and let him/her know what your concerns are and see if they can help. Also, since we are getting to the end of the year - talk to the principal about making sure these two do not have the same class next year - you don't want a repeat.
You can send a note in addressed to the boy's parents. Seal the envelope and ask that it go home with the child. It shouldn't be a problem. My daughter gets things all the time - like invitations, so why would this be any different.
Your daughter is young for first grade - has the teacher talked to you about her academic maturity? Is holding her back a possibility? Would you even be interested? Do you think she would benefit from it?
I also have experience with this - I can tell you my story if it is something you are interested in. Holding your child back is a hard choice and it may or may not be an option for your daughter. Just thought I would put it out there.
Social issues really can affect their school lives. Before my daughter and this other girl clashed - school was great, she loved it. She is at the top of her class. Then one day the other girl got mad and threatened to stab my daughter with her scissors. We stepped in real quick.
We told my daughter that she is NOT to associate with this kid. But it is hard because they are in the same class, eat together, have recess together, same bus, even go to the same after school care. It got really difficult for my child because this other kids is great at manipulation and my daughter ended up being the one playing alone in the corner.
We had to go to a plan B - because she was so out of sorts over it all.
Luckily we have a teacher that works with us and it is getting better.
But I know what it is like having a child come home and say she hates school, has no friends, hates her life, etc. She is 7 - why does she have to deal with this? Everything should be wonderful in life, right?
One child has hindered my daughter's education. We have had to act fast - but tread lightly. How do you keep a child away from yours when you aren't around to police it? They won't let you sit in class with your kid.

It is a difficult balance.
Just continue to communicate with the school. Don't let them brush you off.