I think Daisy sounds like she will be fine. Seperation anxiety, I think, tends to be continous throughout the time apart - an initial cry and then settling down is just normal "If I cry a bit they might come back and play"... Honey doesn't whine when we leave her in her dining room, as she loves the treat she gets too much (!), but does if one of us goes out of range (either upstairs, or into a shop when out). When we stayed at my in-laws after Christmas, we left her with them for a couple of hours and she howled for the first couple of minutes, then was perfectly happy!!!
Have you left her at your Dad's before? If not, can you leave her there for an afternoon, so that she knows being left there doesn't mean being left forever (and you know that she will be happy there)
Good luck - I have to say I was adamant that kennels would be fine for any dog we got, but have signed Honey up for a local pet boarding service, as I just can't imagine leaving her in kennels!!!