my guess is it was probably something to do with Jill being infected with the T-virus, afterall the nemesis doesnt really "bother" with infected unless they are in his way.
If I remember correctly, right back to when RE2 was in development, it got posponed scrapped and redone twice as well as some content cut, which eventually became glued together with other bits to form RE nemesis, this was mainly because of the technology restraints they had to work with made it difficult for them to achieve exactly what they wanted....
In an old magazine article, when RE2 was in stage 1 of development, there was going to be 5 playable characters (Chris, Jill, Claire, Barry and Leon) of course technology restraints caused them to scrap Chris and Barries scenarios from stage 1, and then Jill from stage 2 (her model apparently took a lot of memory)
To make up for the loss of the orginals in RE2, they eventually worked more on Jill's scenario, trying to bring it up to scratch and finish it up, eventually releasing it as RE nemesis (hense why the inventory screen, music and a lot of other things are commonly shared, the inclusion of round-making was orginally pencilled in for RE2, but never saw the light of day until nemesis)
So taking all that into account, it would actually be possible to do a "proper" RE2 remake and include Jill's nemesis scenario in it, as there would be no restraint from the technology like there was back then, and it would be highly viable and possible.
Just my 2 geeky cents ^^