Taking my mare on a 4 mile hack??

Sapphire has been out of work for the past 3 weeks, I just haven't had time for everything, I thought she'd be appreciative of a little pasture time.
Anyway, a friend has invited me out on a hack, she's going to ride 3 or 4 miles and she's offered me to come too. Now, I know 3-4 miles is nothing, but would you think my mare would be up to it? We're doing a 5 mile sponsored ride next month anyway, so it might be good to get her in shape.

Thank-you

I think she should be fine

Even just wandering around grazing in a pasture, a horse walks more than 3 or 4 miles a day. Your horse should have no problem at all.