Sadly yes, it looks like you have to take the fourway path (MC/Parker/Felix/Monica) to get to Monica's lesbian path.
Shortly after you have the option to opt out of the fourway path, which i assume doesn't end the Monica lesbian path.
I don't know why the dev decided to hide her path behind those options...
If i remember correctly back when she was first introduced some people already asked to include her into a lesbian playthrough without the need to fool around with Parker/Felix.
But yeah, i mean you can just skip through those said paths to get to this point and then end the paths individually i assume.