For the life of me I can't recall the formula for calculating the length of a half-wave wire antenna. It really sounds like the two dipole antennas tied together at the
center and feed with coax might really be a good choice.

I did use one of these many years back and seem to recall that I fed it through a balun but not sure of if it was 3 to 1 or just what it was.

I've  had lots of wire antennas over the years and having trouble remembering which was which if you know what I mean.

Louis, does the antenna you're sister is using employ a balun?

Thanks,

Don W6SMB