Without investigating further, I don't think that it's a problem of girls present or not. I exlpain further down why.Another small oddity: whenever I ask Heather to pose, she acts as if there are others at the pool even though I've sent them away. Any idea what the problem might be? (Or any way to reset the relevant variable with the console?)
If you want to check, open the console and check this variable:
list_of_chars_display_3
or if you want: len(list_of_chars_display_3)
Only Heather should be in the list if you send the others away, so length is 1.
Since this list is used to display the characters on screen in a location, I don't see how this could be bugged without you noticing it.
If there is an "alone with girl check", normaly all that is done in the code is:
if len(list_of_chars_display_3) == 1:
...
or > 1 if the inverse is needed