They said she's a 'mandatory hook up' when they where discussing who the main girl is.
You're right, not even a single kiss is forced in the game. You can go the whole thing hooking up with whoever you want, or even not hooking up at all with anyone.
For the curious, the number of lines of text in the script is like this (the leters are the initials of each girl, plus the MC)
* mc has 16,959 blocks of dialogue.
* j has 4,462 blocks of dialogue.
* e has 4,102 blocks of dialogue.
* l has 2,898 blocks of dialogue.
* d has 2,468 blocks of dialogue.
* k has 1,877 blocks of dialogue.
* o has 1,478 blocks of dialogue.
* b has 1,150 blocks of dialogue.
This doesn't take into account the texting because it uses custom functions. Lea has lots of texting, Jen also has some. So, the dialogues of those 2 are, in truth, a bit higher.