Hiya! I think Lily won't like Regulus much, but as long as he's civil and doesn't call her a Mudblood, she won't outright hate him. Heck, she might even like him better than his brother, at this point.
As for Darlene, she and Lily are totally kindred spirits, at least as far as their passion for taking care of people and keeping order in the castle goes. Lily also wants Darlene's job next year, so she probably looks to her both as a role model and friend. :)