Do you think she would react unfavorably if you asked her for one of their numbers? No need to ask for both, since anything you communicate will be shared if they live together. It's easy if you think she would let you have it. If not, if they live close, you could offer to come by sometime over the Christmas holidays to drop off their gift (that you thoughtfully picked out, which hopefully will impress her) to them and say hello. While you are there you could bring up in conversation pretty much anything that you and she do or plan to do together, and then offer to send them photos (if you want to be subtle, do it as an afterthought "oh hey, if you would like, I could text you the pictures I take of us while we..."). Another approach is to offer them your phone number, "just in case they can't get ahold of ____".