I'd just let her have the week off. Unless you think she'll really go bonkers (is she turned out or stalled? Stalled=needs to get out, pasture=let her have the week off) I'd let her have a vacation too! :)
She might miss you - that'll be your reward for coming home! Having a snuggly pony is the best. :)
I'm sure she'll be fine. I've never really left my mare either and I know I would have a hard time leaving her for a full week too. However, I would make myself feel better by making doubley-sure her "horsesitter" knew what they were doing, had everything they could possibly need if things went wrong and everything they could possibly need if things went right, then I would ENJOY my vacation.
I know that the time I did leave Lacey for a weekend, it was a huge relief to have her "babysitter" text me a picture of her and write me a little message about something cute Lacey did that day. A picture a day for a week might be a lot, but maybe you could have someone who's looking after your mare text you a little update everyday or every other day?
And above all, enjoy your vacation! I wish I could have one!