Steve,
Surely you recognize that people’s lives are busy. I think the lady giving you the heads up that she’ll be off to the lake for a week (to me, the implication is that she’s letting you know she may be a bit unresponsive, which is very considerate of her) along with the fact that she sent the notification that she wants to meet you are all positive, good signs. You might wonder why she’s still logging onto the site if she’s not responding to you. One thing to consider is that the level of effort required to log in and take a look around is a lot lower than the effort required to respond to messages. I have my email up all day at my desk, and I respond to emails as I feel the desire to write back. I would hate for any of my friends to think that the timeliness of my response has any correlation to my affection for them as people. “But she has her email up all day, why isn’t she writing back?” If there were something that demanded an expedited response (“Do you want to go to the ball game tonight?”) I would respond immediately. However, a general “here’s a download of stuff going on in my life, how are you doing?” shouldn’t make a person feel pressured to respond, despite whatever else they have going on. In your case, you telling the gal to have a fun time likely put a smile on her face. She wants to meet you. She knows she won’t be able to meet you until she returns from the lake. Don’t invest so much into hearing back a “thank you, talk to you soon!”

I would avoid asking her if she’s still interested, and rather just throw an invitation out there. “Would you like to meet for coffee next Thursday?” or whatever. Let her response to an invitation be your guide to if she is interested. For what it’s worth, one of the reasons I do not participate in online dating is because of the pressure I feel from guys who are very eager and get worked up over not getting immediate responses, or who make assumptions about my level of interest based on relatively benign indicators (logging in but not responding, for example). Understand from a woman’s point of view, we get TONS of messages to respond to and frankly, it’s a lot of work. Good things come to those who wait. In the meantime, ask out the other lady and see how things go.