Leda was at the Crossroads to do a job. She was hooking up the WiFi and thinking about getting home. A special request from the Guardians diverted her plans and had her working at the side of a lovely merman, but she still wanted to head home. She wasn't seeking a mate and didn't care that he was.
Altion was surprised by the strong and competent young woman that Teal directed him to, but Leda did what she had promised and helped him craft what he needed to make the site-to-site portal for the Isthmus.
A magical snafu links them together and finding a way through the changes is not as hard as finding neutral ground between the lake and the sea.