take your time with her, I know how hard that sounds after you've been without any stimuli for so long but if you just shove it in it likely won't feel too good, warm her up with your tongue/fingers, then go slow and steady with her until she can handle you.
lube is unneeded as the vagina has so much natural lubricant anyway, however if your on the larger side and she doesn't have too much experience you could get her some toys to stretch her out a little.