Yes, I feel she reached her peak around episodes 7-8 then fell off from there. I looked at some of the earlier episodes and the quality was definitely better but I'm not sure how much that is affecting her looks. Doubt this will affect the ship much anyway but glad I'm not the only one who noticed.
Yeah I really don't think her looks will affect the ship. I really think she just needs to put herself out there and interact with Ash more often in general to catch his attention because quite frankly, I don't think Ash cares much about how girls look. He seems to become more interested in girls when they show interest in him, so I think Serena's best course of action is to get to know Ash a little more. I mean they barely know anything about each other, so progress could always be made.