If you and they are on facebook, you can do videochats on that, which seems to work reasonably well.
It's not quite as extreme as your daughter in New Zealand, but as you know I'm at university 200 miles from my family. I don't like to bother them too much (as it is always my Dad, since my mum doesn't even have a mobile phone!) but something that we do is if we see a joke, or a picture, or an article that I think they might like or be interested in, I send it to them. It's just a little thing that says "I am thinking of you". Even if the only response is a smiley face, on the worst days it is like gold dust.
Remember that depression is a nasty little voice in the back of your brain that always makes you assume the worst. You feel like everybody hates you or is out to get you, and the voice feeds that. Definitely try to talk to your daughters a little bit about how you feel. As a child, I would say that I didn't realise, or still don't realise, everything that my parents do and have done for me, and how they might feel, until I have been through that myself. We take our parents for granted so much, sometimes we need to be reminded.
Rabbit away. We are here to listen, and besides, it's better out than bottled up inside you where it will only do more damage.
You are so strong Maggie. Sending you more hugs.