The so called saved the life of Rosie was only in one brief incident , in the school as compare to the other characters…
Example We met Kwlly from the beginning , then had scene of saving her from Markarov to other svene of interaction that could increase the relationship stat …
I suppose same could said about Woody
And in this case, i had once said the relationahip.stat is a good technical indication on why a RO would love us, it gives indication on whether our encounters were enough to bond us together…
Hence in order to romance Kelly and Woody , there would be enough relationahip to do that , same like Bailey…
For Rosie, the logical thinking is that when she shot at us , it minus the bond, and minus again if we save Jillian from her, we saved her was a plus… hence , it is something like minus plus equal zero, minus minus plus equal minus… there simply not enough encounter to make the bonds yet…
Well that is my opinion though 
@CreoleGuy519, that’s depend on the relationship stat as well… Gina was usually low relationship with me , even after i saved her… Rachel, as in same circumstance , had more encounters to raise our relationship with her … else we couldn’t romance them as well right ?
Well the point is, there should be more occasions to raise Rosie stat before she could logically loves us , well that is my assumption… and my relationship with her was low as well even after i allow her to join us
Edit : haha @JimD clarify the whole situation for us already :-)