Ahhhhh, the wonderful age of 13. If I could write a letter to my 13 year old self, I would have so much advice for her.
As far as switching pumps - I think it would be more difficult to conceal any other kind of pump under a bathing suit with the tubing and whatnot. I wear a MiniMed, so on the rare occasions that someone can convince me to wear a bathing suit, I put my site in my butt so it will be covered and out of view. But of course, then I have to clip the pump itself somewhere...Does the omnipod allow you to hook it up in a place that would be covered?
For "all day at the beach" situations, it is perfectly acceptable to disconnect from the Pod completely and use a long acting insulin for the day. This might be the best starting off point with your daughter.
Also, is there a way for her to get involved in diabetes camp? At 13, she might be old enough to be a junior counselor. Being a role model for younger kids with Type 1 diabetes could really improve her outlook on the whole situation.
Lastly (and you may not want to hear this) consider allowing your daughter to take a "pump break." Maybe 6 or 7 months was not enough time to adjust to the initial diagnosis...Being a teenager and coming to terms with diabetes can be overwhelming already, and then add a medical device to your body, and well...It can just all become too much to handle.