Darn, other horses generally help.... how long has it been? Not all horses "read the How-to-be-a-Horse book" and react the same, but I have found that two weeks is generally the magic number.
However, I take any new Momma and her threats very seriously.
Can you do all her feeding close to the fence line to keep an eye on her? If you are having a hard time getting close to the foal, it's still important to see and be seen. Do lots of pasture chores.
One way is to try to separate Momma and filly ( very strong fence, I hope.) How you manage that..... well, good luck, huh? While Momma gets upset, kneel in the center of the filly's area. The filly should run to Momma at first, then when you don't move, she should come to investigate you. Try not to separate them for more than ten minutes or so. Repeat several times a day if possible. That may be impossible to do, sorry for the lack of help.
You don't know any history on the dam, right? First foal? Maybe last foal weaned too early? Maybe this is just normal behaviour for Momma?